Starting stack seems pretty generous (280BB) to start with considering you blind structure. Your blinds do seem to get more aggressive later on but I'd guess at minimum this tournament would take 4-5 hours, very possibly longer depending on player types (tights vs maniacs). Your going 2hrs and 40 minutes (5 rounds with 2 breaks) and your BB is only 1/14 of the starting stack.
My gut would be to skip the 5/10 level and go right to 10/20 or switch the starting round times from 20 to 30 minutes and ending round times from 30 to 20 minutes. Usually rounds get shorter as the tournament progresses because there are less people so folks are still seeing roughly the same number of hands in less time.
Here is some more info on estimating tourney length from HPT
http://www.homepokertourney.com/blinds.htm. Method 3 says the tourney should end when your BB is between 2240 - 4480 which easily pushes you into 6hrs in your current setup.
