Time data is stored as integers, actually, and the formatting is done on the client side. When you say web form, is this Survey123 or Field Maps? Or something else?
I personally enter all of my data in 24-hour format, and it usually takes something like "13:45" and interprets it as 1:45 PM automatically, but I'm not often using the field apps.
- Josh Carlson
Kendall County GIS