I have seen Ariane-5 lift off at T+07 seconds and not at (or close to) T=00 seconds. The following statement is from the Ariane-5 User's Manual (Page 35, Section 2.3 - Typical Mission Profile):
The engine of the cryogenic main core stage, Vulcain 2, is ignited at H0+1s. Until H0+7.05 seconds, the on-board computer checks the good behavior of the engine and authorizes the lift-off by the ignition of the two solid rocket boosters.
Most of the rockets to the best of my knowledge lift-off exactly (or around) T=00 seconds. Engine ignition takes place at somewhere like T-0x seconds. Then they attain full thrust close to T=0 seconds. Either SRBs ignite and hold down clamps release or the launch clamps release and lift-off take place. Why does Ariane-5 liftoff at T+7.05 seconds instead of T=0 seconds? Why so much delay? Instead, they could have started the engine ignition and the following checks a bit earlier (like engine ignition at T-6.05 seconds, and SRB ignition and lift-off at T=00 seconds). What is the reason for this? Are there any other launch vehicles which lift-offs well after T=00 seconds?
I thought all Ariane Space launch vehicles (Soyuz, Vega, Vega-C, etc.) do the same thing, but the following ascent profile of Soyuz shows that it lifts-off at T=00 seconds.
(Image from Soyuz User's Manual - Page 35)