Only timestamp is usefull, no need to build a Date.

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/factories/event/TimelineItemEventFactory.kt

@@ -146,10 +146,9 @@ class TimelineItemEventFactory(
                 senders = reaction.senders
                     .sortedByDescending { it.timestamp }
                     .map {
-                        val date = Date(it.timestamp)
                         AggregatedReactionSender(
                             senderId = it.senderId,
-                            timestamp = date,
+                            timestamp = it.timestamp,
                             sentTime = dateFormatter.format(
                                 it.timestamp,
                                 DateFormatterMode.TimeOrDate,

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/model/AggregatedReactionProvider.kt

@@ -33,13 +33,14 @@ fun anAggregatedReaction(
     val timeFormatter = DateFormat.getTimeInstance(DateFormat.SHORT, java.util.Locale.US).apply {
         timeZone = TimeZone.getTimeZone("UTC")
     }
-    val date = Date(1_689_061_264L)
+    val timestamp = 1_689_061_264L
+    val date = Date(timestamp)
     val senders = buildList {
         repeat(count) { index ->
             add(
                 AggregatedReactionSender(
                     senderId = if (isHighlighted && index == 0) userId else UserId("@user$index:server.org"),
-                    timestamp = date,
+                    timestamp = timestamp,
                     sentTime = timeFormatter.format(date),
                 )
             )

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/model/AggregatedReactionSender.kt

@@ -7,16 +7,12 @@
 
 package io.element.android.features.messages.impl.timeline.model
 
-import androidx.compose.runtime.Immutable
 import io.element.android.libraries.matrix.api.core.UserId
 import io.element.android.libraries.matrix.api.user.MatrixUser
-import java.util.Date
 
-// Need to be marked as @Immutable for Date
-@Immutable
 data class AggregatedReactionSender(
     val senderId: UserId,
-    val timestamp: Date,
+    val timestamp: Long,
     val sentTime: String,
     val user: MatrixUser? = null
 )