Fit precisely elements in the calendar

I'd like to be able to be more precise about time blocking i.e. if I have tasks that I estimate to take 10min and 5min I'd like to be able to pull them into the calendar without them overlapping. For example task A (10min) fits into the calendar from 2pm until 2:10pm and after that task B (5min) fits into the calendar from 2:10pm until 2:15pm. Currently, all tasks take up 15min blocks.