Oooh... that's a good one. So you're using a DateTime field. Someone will enter 18:07 (which is 6:07pm) and you want that to be rounded UP or DOWN to the nearest 15 minute increment? I already cover converting a difference in times to hours:minutes in my Calculate Total Time video, but the rounding part is new.

Round to nearest
http://599cd.com/blog/display-article.asp?ID=1063

Round to Nearest Multiple
Expert 26 - Lesson 1
https://599cd.com/site/courselist/access2013/expert/x26/

Rounding is a very good option. I was hoping to enter a validation rule that warns them they must enter time in 15-minute increments and let the user fix it, instead of automatically rounding. I don't know how to structure the validation test.

OK, I got this. :)

Here ya go, Sharon: 15-Minute Increments.

This is so cool and you did it so quickly. Thank you. Exactly what I wanted

You happened to catch me at exactly the right time. I was drinking my coffee, looking over the mountain of TechHelp questions I have from other students, and I was trying to decide which one to answer. Then I saw your question, and I was like... ooohhh... that's a good one. I haven't done anything like this in a lesson before. Sometimes I like a challenge too. :)