You can probably mow a day later but I always mow first so I don't have to worry about it because then I won't be mowing again for 4 or 5 days.

Could mowing in advance cause a similar problem in that you reduce the surface area that the chemical can affect?

Let the weeds grow tall, dont mow, apply weedbgone and then DONT MOW. Wait at least a week because the chemicals are in the leafs killing the plant. If you mow right away so weeds will come back.

I mow before I spray but I mow on the highest setting so a lot of the leaves of the weeds are left to absorb the chemical. I haven't had any problems and the weeds usually still die off. I mostly just have the ground ivy stuff which is a pain to kill and I sometimes have to spray it twice if I have to, once to stun it then a 2nd like a week later to kill it.