When you are trying to plan yor day, there are like 3 time default options ( for example:- 12, 3 and 7). Without considering if you already have something scheduled for that time-block:
a.- Task situation: If i set the first task of the list at 12, it could be a nice functionality that in the second one "time default options" instead of (12, 3 and 7) could be substituted for (1,3 and 7).
b.- Event situation: If already have an event for that time block, it shouldn´t suggest that time to set a reminder during moment.