Date and Time Limit

Can I limit what time is select in a Date\Time field based on another Date\Time field? Our app has one field that starts a record, then a second date and time that is based on that first one. I want to only give users the option to select a time 2 hours after the first time and also set a limit, like 5:00 PM. So for example, if the request was started at 8:00 AM, then the second time can only be from 10:00 AM to 5:00 PM. Please help. This is a big request we have. Users are selecting wrong hours even though they know they have a 2 hour gap that needs to be filled first. Thank you.

This is likely possible with Javascript.

Point of Clarification - is that FIRST Time already on the recorded and saved, or is a time that the user is selecting before selecting the first time?