Length of day?

Newbie question here - only at Summer 11 of Year 1.

I get kinda frustrated with how quickly the days go by trying to do everything even though I have a mount and the water bucket so far. I saw in the options you can change the length of the day from 15 minutes (which shows recommended) to either 17.5 minutes or 20 minutes. Anyone done this yet? If so, did you notice and benefit or disadvantages? Thanks in advance!