Improve the accuracy of duration calculations in cron jobs monitoring (#2471)

* Update monitor_check_ins.rb
* Update CHANGELOG.md

---------

Co-authored-by: Peter Solnica <peter@solnica.online>

Author: krzysztofjablonski

CHANGELOG.md

@@ -16,6 +16,7 @@
 - Add support for string errors in error reporter ([#2464](https://github.com/getsentry/sentry-ruby/pull/2464))
 - Reset `trace_id` and add root transaction for sidekiq-cron [#2446](https://github.com/getsentry/sentry-ruby/pull/2446)
 - Add support for Excon HTTP client instrumentation ([#2383](https://github.com/getsentry/sentry-ruby/pull/2383))
+- Improve the accuracy of duration calculations in cron jobs monitoring ([#2471](https://github.com/getsentry/sentry-ruby/pull/2471))
 
     Note: MemoryStore and FileStore require Rails 8.0+
 

sentry-ruby/lib/sentry/cron/monitor_check_ins.rb

@@ -14,12 +14,12 @@ def perform(*args, **opts)
                                                 :in_progress,
                                                 monitor_config: monitor_config)
 
-          start = Sentry.utc_now.to_i
+          start = Process.clock_gettime(Process::CLOCK_MONOTONIC)
 
           begin
             # need to do this on ruby <= 2.6 sadly
             ret = method(:perform).super_method.arity == 0 ? super() : super
-            duration = Sentry.utc_now.to_i - start
+            duration = Process.clock_gettime(Process::CLOCK_MONOTONIC) - start
 
             Sentry.capture_check_in(slug,
                                     :ok,
@@ -29,7 +29,7 @@ def perform(*args, **opts)
 
             ret
           rescue Exception
-            duration = Sentry.utc_now.to_i - start
+            duration = Process.clock_gettime(Process::CLOCK_MONOTONIC) - start
 
             Sentry.capture_check_in(slug,
                                     :error,