The 'Best Time To Call' option is too limited as it only allows you to set a single point in time, however, you will contact that person outside of pre-arranged calls, so the ability to add other options would be very helpful.

For example one of my best contacts only works Wednesdays 10-4 and Fridays 8-5, those are the best (and only) times to contact her.

Perhaps that box could be split, so the first is 'Next call' which shows the date of the next activity/call/meeting, and the second is 'Best time to call' which allows the selection of multiple weekdays (not dates) and times for each of those days.