Can you only schedule posts for 5 minute intervals on Socialdraft?

Yes, Socialdraft only allows to schedule posts for 5 minute intervals.

Why? The reason it's in 5 minutes is because of 2 reasons:

1.  Most of the API run in a cycle, so as to not get flagged and rejected by say Twitter or Facebook. Both have very strict rules about amount of posts. This is standard on every system out there.

2. The 5 minutes isn't actually 5 minutes.  It's a queue so sometimes it's  2 minutes and 10 seconds for example and sometimes it's 6 minutes.  All depends on the queue with the 3rd party API. So it won't literally be 5 minutes, but give or take seconds or even minutes depending on the queue.