Ugh. I am starting to get really annoyed by DH's job.
If I were you, I'd take a night or two off in between. Maybe try every other night? BD on 2 days before on, skip 1 day before O, and BD on day of O. Or, surprise him in the morning after a night off.
Forgot to add something... If you think you can only get some once, I'd go for the day before O. He sounds to tired to do it tonight. Plenty of babies are conceived as "one hit wonders" so don't feel too stressed about getting it in every night.