Damage that a dot effect deals is calculated each time a tick happens not during initial application.
In other words, if you pop an adrenal / relic / ability halfway through a dot's duration the remaining ticks would get affected by them.
Going from that it is safe to say that battle focus's effect is added to damage calculations by the time assault plastique/sticky grenade actually deals its damage.
TL;DR : Yes using battle focus after you have used grenades will still give you increased crit chance.
That's what I was thinking I just wasn't sure. Thanks.