If you DO have power brakes, indeed the vacuum unit is suspect: It's not getting it's vacuum quickly enough, or little or no vacuum was available? It's leaking somewhere, check valve, cracked vacuum hose, or just plain old bad unit.
Some other possibilities (especially if you DON'T have "power brakes") are:
The pistons in the calipers retracted to far back in there bore, while the car was sitting?
The piston cups in the master cylinder didn't seal right away (again due to sitting?) and the first pedal stroke or two was not effectivly building pressure?
Either way the end result would be a low hard pedal until the second or third stroke. The key here is, HOW low did the pedal go?
The symptoms described (low, hard pedal) would support such a theory. First stroke of the brake pedal pushes the pistons back into place, but the master cylinder piston has reached full stroke, it's hard, but cannot build up any more pressure. Second stroke (or third stroke) would apply pressure now that the pistons are in position closer to the rotor.
OR, second ot third stroke would establish a good seal in the master cylinder piston and pressure would THEN be available.
Ernie
This link just in from another thread! Excellent stuff here!
http://www.911brakes.com/