Add calendar event

If I know that the task I would like to enter to OF will take time from 3 pm to 5 pm, what do I need to do to make it appear as calendar events in Forecast view? Can I do it from within OF?

Calendar events on OF Forecast come from Calendar, and not from the app’s database.
If you want them in that view, you have to add it to your Calendar — which, for me, it’s where appointments (tasks which are time bound) belong to ;-)