The weatherman was wrong... Weedkillers

[MayDayChild]

So I slathered weedkiller all over my gravel drive about 12 midday Sunday.
It poured this morning unexpectedly.
Was 40 hours long enough for it to work?

I've just done mine and noticed on the bottle it said it needed 12 hours with no rain, so you should be ok I think surely 40 would be enough for the weeds to absorb the killer regardless of brand etc. Good luck