diff --git a/src/client/batch.ml b/src/client/batch.ml
index e5f7c88f..40e17a22 100644
--- a/src/client/batch.ml
+++ b/src/client/batch.ml
@@ -18,13 +18,14 @@ let max_batch_size = 100_000
 let default_high_watermark batch_size =
   max 10 (min (batch_size * 10) max_batch_size)
 
-let _dummy_start = Mtime.min_stamp
+(** passed to ignore timeout *)
+let mtime_dummy_ = Mtime.min_stamp
 
-let _empty_state : _ state = { q = []; size = 0; start = _dummy_start }
+let _empty_state : _ state = { q = []; size = 0; start = mtime_dummy_ }
 
 let[@inline] cur_size (self : _ t) : int = (Atomic.get self.st).size
 
-let make ?(batch = 100) ?high_watermark ?now ?timeout () : _ t =
+let make ?(batch = 100) ?high_watermark ?mtime ?timeout () : _ t =
   let batch = min batch max_batch_size in
   let high_watermark =
     match high_watermark with
@@ -34,9 +35,9 @@ let make ?(batch = 100) ?high_watermark ?now ?timeout () : _ t =
   assert (high_watermark >= batch);
 
   let start =
-    match now with
+    match mtime with
     | Some x -> x
-    | None -> _dummy_start
+    | None -> mtime_dummy_
   in
   assert (batch > 0);
   {
@@ -46,22 +47,19 @@ let make ?(batch = 100) ?high_watermark ?now ?timeout () : _ t =
     high_watermark;
   }
 
-(** passed to ignore timeout *)
-let mtime_dummy_ = Mtime.min_stamp
-
-let timeout_expired_ ~now ~timeout (self : _ state) : bool =
-  now <> mtime_dummy_
+let timeout_expired_ ~mtime ~timeout (self : _ state) : bool =
+  mtime <> mtime_dummy_
   &&
   match timeout with
   | Some t ->
-    let elapsed = Mtime.span now self.start in
+    let elapsed = Mtime.span mtime self.start in
     Mtime.Span.compare elapsed t >= 0
   | None -> false
 
 (** Big enough to send? *)
 let[@inline] is_full_ ~batch (self : _ state) : bool = self.size >= batch
 
-let pop_if_ready_ ~force ~now (self : _ t) : _ list option =
+let pop_if_ready_ ~force ~mtime (self : _ t) : _ list option =
   let rev_batch_opt =
     (* update state. When uncontended this runs only once. *)
     Util_atomic.update_cas self.st @@ fun state ->
@@ -72,7 +70,7 @@ let pop_if_ready_ ~force ~now (self : _ t) : _ list option =
       state.size > 0
       && (force
          || is_full_ ~batch:self.batch state
-         || timeout_expired_ ~now ~timeout:self.timeout state)
+         || timeout_expired_ ~mtime ~timeout:self.timeout state)
     in
 
     if ready_to_pop then (
@@ -89,8 +87,8 @@ let pop_if_ready_ ~force ~now (self : _ t) : _ list option =
     (* Reverse the list to retrieve the FIFO order. *)
     Some (List.rev batch)
 
-let pop_if_ready ?(force = false) ~now (self : _ t) : _ list option =
-  pop_if_ready_ ~force ~now self
+let pop_if_ready ?(force = false) ~mtime (self : _ t) : _ list option =
+  pop_if_ready_ ~force ~mtime self
 
 let push (self : _ t) elems : [ `Dropped | `Ok ] =
   if elems = [] then
@@ -128,8 +126,8 @@ let[@inline] push' self elems = ignore (push self elems : [ `Dropped | `Ok ])
 open Opentelemetry_emitter
 
 (** Emit current batch, if the conditions are met *)
-let maybe_emit_ (self : _ t) ~(e : _ Emitter.t) ~now : unit =
-  match pop_if_ready self ~force:false ~now with
+let maybe_emit_ (self : _ t) ~(e : _ Emitter.t) ~mtime : unit =
+  match pop_if_ready self ~force:false ~mtime with
   | None -> ()
   | Some l -> Emitter.emit e l
 
@@ -146,7 +144,7 @@ let wrap_emitter (self : _ t) (e : _ Emitter.t) : _ Emitter.t =
       (* NOTE: we need to close this wrapping emitter first, to prevent
          further pushes; then write the content to [e]; then
          flusn and close [e]. In this order. *)
-      (match pop_if_ready self ~force:true ~now:Mtime.max_stamp with
+      (match pop_if_ready self ~force:true ~mtime:mtime_dummy_ with
       | None -> ()
       | Some l -> Emitter.emit e l);
 
@@ -155,13 +153,13 @@ let wrap_emitter (self : _ t) (e : _ Emitter.t) : _ Emitter.t =
     )
   in
 
-  let tick ~now =
+  let tick ~mtime =
     if not (Atomic.get closed_here) then (
       (* first, check if batch has timed out *)
-      maybe_emit_ self ~e ~now;
+      maybe_emit_ self ~e ~mtime;
 
       (* only then, tick the underlying emitter *)
-      Emitter.tick e ~now
+      Emitter.tick e ~mtime
     )
   in
 
@@ -172,7 +170,7 @@ let wrap_emitter (self : _ t) (e : _ Emitter.t) : _ Emitter.t =
       (* we only check for size here, not for timeout. The [tick] function is
          enough for timeouts, whereas [emit] is in the hot path of every single
          span/metric/log *)
-      maybe_emit_ self ~e ~now:mtime_dummy_
+      maybe_emit_ self ~e ~mtime:mtime_dummy_
     )
   in
 
diff --git a/src/client/batch.mli b/src/client/batch.mli
index 88a5dfc0..706f4167 100644
--- a/src/client/batch.mli
+++ b/src/client/batch.mli
@@ -5,7 +5,7 @@ type 'a t
 val make :
   ?batch:int ->
   ?high_watermark:int ->
-  ?now:Mtime.t ->
+  ?mtime:Mtime.t ->
   ?timeout:Mtime.span ->
   unit ->
   'a t
@@ -21,15 +21,15 @@ val make :
       transmission in case of signal floods. Default
       [if batch = 1 then 100 else batch * 10].
 
-    @param now the current time. Default [Mtime_clock.now ()].
+    @param mtime the current time.
 
     @param timeout
       the time span after which a batch is ready to pop, whether or not it is
       {b full}. *)
 
-val pop_if_ready : ?force:bool -> now:Mtime.t -> 'a t -> 'a list option
-(** [pop_if_ready ~now b] is [Some xs], where is [xs] includes all the elements
-    {!push}ed since the last batch, if the batch ready to be emitted.
+val pop_if_ready : ?force:bool -> mtime:Mtime.t -> 'a t -> 'a list option
+(** [pop_if_ready ~mtime b] is [Some xs], where is [xs] includes all the
+    elements {!push}ed since the last batch, if the batch ready to be emitted.
 
     A batch is ready to pop if it contains some elements and
 
@@ -39,7 +39,7 @@ val pop_if_ready : ?force:bool -> now:Mtime.t -> 'a t -> 'a list option
       the last pop was ready, or
     - the pop is [force]d,
 
-    @param now the current time
+    @param mtime the current monotonic time
 
     @param force
       override the other batch conditions, for when when we just want to emit