Hi,
I've just carried out the upgrade to 1.15.4 and everything went through smoothly. I've spent a bit of time setting up work schedules and SLA's but they don't appear to be working quite as expected.
I've had a read through the help pages and they reference the timeline diagnostics tool that should give some verbose output but I can only see the date time and the hours fields.

I noticed the issue because I have set up the schedule to be from 9am to 5pm GMT and set the default ticket SLA to 1 hour for an initial response. I logged a ticket at 3pm and the due date has returned as 18 hours time rather than an hour.
The server is running Cpanel with PHP 7.4.
Thank you in advance,
Chris