diff --git a/temporalio/lib/temporalio/contrib/open_telemetry.rb b/temporalio/lib/temporalio/contrib/open_telemetry.rb
index a894e300..e39886f3 100644
--- a/temporalio/lib/temporalio/contrib/open_telemetry.rb
+++ b/temporalio/lib/temporalio/contrib/open_telemetry.rb
@@ -455,13 +455,12 @@ def self.completed_span(
           # Create span, which has to be done with illegal call disabling because OTel asks for full exception message
           # which uses error highlighting and such which accesses File#path
           Temporalio::Workflow::Unsafe.illegal_call_tracing_disabled do
-            time = Temporalio::Workflow.now
-            timestamp = (time.to_i * 1_000_000_000) + time.nsec
-            span = root.tracer.start_span(name, attributes:, links:, start_timestamp: timestamp, kind:) # steep:ignore
+            time = Temporalio::Workflow.now.dup
+            span = root.tracer.start_span(name, attributes:, links:, start_timestamp: time, kind:) # steep:ignore
             # Record exception if present
             span.record_exception(exception) if exception
             # Finish the span (returns self)
-            span.finish(end_timestamp: timestamp)
+            span.finish(end_timestamp: time)
           end
         end
       end
diff --git a/temporalio/test/contrib/open_telemetry_test.rb b/temporalio/test/contrib/open_telemetry_test.rb
index fed1eaa1..bc9f2c3e 100644
--- a/temporalio/test/contrib/open_telemetry_test.rb
+++ b/temporalio/test/contrib/open_telemetry_test.rb
@@ -143,6 +143,7 @@ def trace(
       tracer_and_exporter: init_tracer_and_exporter,
       always_create_workflow_spans: false,
       check_root: true,
+      append_finished_spans_to: nil,
       &
     )
       tracer, exporter = tracer_and_exporter
@@ -160,6 +161,7 @@ def trace(
       end
 
       # Convert spans, confirm there is only the outer, and return children
+      append_finished_spans_to&.append(*exporter.finished_spans)
       spans = ExpectedSpan.from_span_data(exporter.finished_spans)
       if check_root
         assert_equal 1, spans.size
@@ -174,9 +176,10 @@ def trace_workflow(
       start_with_untraced_client: false,
       always_create_workflow_spans: false,
       check_root: true,
+      append_finished_spans_to: nil,
       &
     )
-      trace(tracer_and_exporter:, always_create_workflow_spans:, check_root:) do |client|
+      trace(tracer_and_exporter:, always_create_workflow_spans:, check_root:, append_finished_spans_to:) do |client|
         # Must capture and attach outer context
         outer_context = OpenTelemetry::Context.current
         attach_token = nil
@@ -318,7 +321,8 @@ def test_handler_failures
 
     def test_activity
       exp_root = ExpectedSpan.new(name: 'root')
-      act_root = trace_workflow(:wait_on_signal) do |handle|
+      raw_finished_spans = []
+      act_root = trace_workflow(:wait_on_signal, append_finished_spans_to: raw_finished_spans) do |handle|
         exp_cl_attrs = { 'temporalWorkflowID' => handle.id }
         exp_run_attrs = exp_cl_attrs.merge({ 'temporalRunID' => handle.result_run_id })
         exp_start_wf = exp_root.add_child(name: 'StartWorkflow:TestWorkflow', attributes: exp_cl_attrs)
@@ -375,6 +379,11 @@ def test_activity
                      handle.execute_update(TestWorkflow.update, :call_local_activity, id: 'my-update-id2')
       end
       assert_equal exp_root.to_s_indented, act_root.to_s_indented
+
+      # Confirm the custom in-workflow span time is within 5m of the given time
+      custom_span = raw_finished_spans.find { |span| span.name == 'custom-workflow-span' } || raise
+      assert_equal custom_span.start_timestamp, custom_span.end_timestamp
+      assert_in_delta Time.now, Time.at(0, custom_span.start_timestamp, :nanosecond), 5 * 60.0
     end
 
     def test_client_fail
diff --git a/temporalio/test/sig/contrib/open_telemetry_test.rbs b/temporalio/test/sig/contrib/open_telemetry_test.rbs
index 9043264d..b1eae7f7 100644
--- a/temporalio/test/sig/contrib/open_telemetry_test.rbs
+++ b/temporalio/test/sig/contrib/open_telemetry_test.rbs
@@ -4,14 +4,16 @@ module Contrib
     def trace: (
       ?tracer_and_exporter: [untyped, untyped],
       ?always_create_workflow_spans: bool,
-      ?check_root: bool
+      ?check_root: bool,
+      ?append_finished_spans_to: Array[untyped]?
     ) { (Temporalio::Client) -> void } -> untyped
     def trace_workflow: (
       Symbol scenario,
       ?tracer_and_exporter: [untyped, untyped],
       ?start_with_untraced_client: bool,
       ?always_create_workflow_spans: bool,
-      ?check_root: bool
+      ?check_root: bool,
+      ?append_finished_spans_to: Array[untyped]?
     ) { (Temporalio::Client::WorkflowHandle) -> void } -> untyped
 
     class ExpectedSpan