I am new in the game and I have the following question. As you can see in the following flight plan, I have plenty of space to add one or two flights. This flight plan runs almost for one week. If I add new routes in this FP what option should I choose? Activate Plan or Activate Plan (3 days delay)?
Activate Flight Plan - not the (3 days) option. The latter is the one you would choose if you had flights that replace other existing segments in your flight plan.
Also, you can gain a few minutes by moving the PHL-LAS segment up by 6 minutes and by preponing the ORD-PHL segment to 20:52 hub time. Both changes will not affect those flights that have already been activated, while giving you a few extra points of maintenance.