Your Early Return through Alamo will apply if you are a Calendar day Early...and it's a flat $15 not $15 per day. You are charged only the days you had the car and the early return fee.
If you had a Minimum keep requirement, the base rate can change.

If you aren't quoted a Drop Fee, you won't be assessed a Drop Fee when you rent, Peter is correct.

Your description of the :30's is a New one on me. I've not seen that one before. I've seen the rates change on the Minimum keep requirements not met but Never ever in 11 years have I seen rates change because of the :30 booking issue.

You've got my curiosity up now though. That's one wackie weirdness I've never heard before. And believe me I've seen some strange things.

P