This is a great question! You can set default values (that can be overwritten) in number, currency, percent, and single line text fields, but this may not be exactly the answer you’re seeking since you’re looking to set default times.
Can you provide some more detail about how your table is structured? This could help us provide a bit more structured guidance. If you’d rather not post about it in this forum, we’d encourage you to contact firstname.lastname@example.org, where we can help you 1-to-1.