When I set up my first repeater, I had both a raising bridge and a retracting bridge connected to the same pressure plate, and when the pressure plate got water on it, the raising bridge raised on one tick and the retracting bridge opened one tick later. When I replaced the retracting bridge with a second raising bridge, they both activated simultaneously.
Oookay, I just did this same test, and the retracting bridge opens one tick earlier for me. There's some variable here we're not taking into account.
EDIT: And yes, pressure plates add one tick to raise times. It's because a lever starts the "Open" order at t=0 after activation, but a PP starts it at t=1.
Just did the same test, and got them both opening on the same tick :/ . Hmm... Does the size of the bridge have any effect? Distance from the trigger? Mechanic skill of the dorf connecting them? It doesn't seem like any of these have any effect, from what I've seen while testing different designs, but I wasn't explicitly watching for it then.
It seems more that pressure plates, at least when using fluids, require that it sit on the plate for one tick before they count as triggered. I could be wrong there, but that would explain the delay.
The best design I came up with so far ends up at 301 ticks. 101 off, 200 on. That doesn't make sense to me, but that's what I got every time I counted, watching a door that was also linked to the plate. It uses two pumps, a retracting bridge, a raising bridge, and one plate, and could theoretically be run with only a single 7/7 block, if you added more pumps to bring it back to the start rather than letting it be destroyed by the raising bridge.
1 2
XXX XXX
R>>PX >>DX
XXX XXX
Where R is the retracting bridge, D is the drawbridge, P is a pressure plate set to trigger on 0-4 water (magma should work just fine as well). P is linked to both bridges.
Of course, that only works assuming both bridges switch at the same time. Which is all I've observed on my testing map :/ .
I tried altering the period of that repeater, by switching out the bridges for hatches and doors, and building a small inverter operating on the same principles, except I wound up with all the doors opening on the tick it was triggered, with the hatches closing three ticks later, even though it should have all happened simultaneously :/ .