I always just write 11:59 P.M or 11:59 A.M. to make this less confusing. Especially because the people setting the time are prone to making the same mistake when scheduling the event.

For example:

...the discount expires at 11:59 P.M. on Thursday, March 24, 2022.

is far less confusing than:

...the discount expires at 12:00 A.M. on Friday, March 25, 2022.

At a quick glance, it's easy to think this means late Friday night, since we see the word Friday.