Me too !
I think like you I always think "oh I'll just get this done 1st".
One of the tips from Flylady (see GH threads) is to always allow WAY more time than you think you need.
Seems like a waste of time, but they advise having stuff in the car that you can do (ie office in a bag - bills to pay, cards to write, menu planner).
So then when you arrive early, you can still get stuff done.
Or if something unforseen happens, you are not late.
(have yet to put all this into practice - in fact am late for lunch NOW!=)