Dual tank, what 2 x 10 Ltrs? on nitrox, you could be down for hours.

Do you ever use a pony rig. I've my stab set-up with one a small 7 ltr job nice little added security.

Hope you get to meet those deadlines, I know the feeling, I have an offer to finish for a power station by the end of March, not enough hours in the day.