With no CDR, if Annie leads with a Stun (Tibbers preferably), QEW + 4 seconds to Q (second stun) + 4 seconds for another Q and W, +2 seconds for another E and finally +2 seconds for a final Q (third stun). 12 seconds if Annie had all spells available and has the mana to back that up at Lvl 6, as well as the presence of game and positioning to pull that off. Note that she doesn't have to land her W, just use it to build up another stun.
But seriously, if your gank starts with being stunned... should probably reconsider.
Edit: Support Annie at lvl 6 probably is lvl 3 Q, lvl 1 WER so the Mana cost on that is 100+70+70+20+70+70+70+20+70 = 560. Her base stats at lvl 6 are 530, so she should OOM before pulling this off.