Trimec is a great broadleaf herbicide. Hovever creeping charlie many times needs two applications timed about 2 weeks apart. The best time to spray it is in early spring before it gets hot. You may get away with only 1 application during this time. It gets extremely hardy as the season progresses. You can use I believe it's called super trimec during the summer if you have any POST-emergent problems with crabgrass. However you must use it in below 85 degree temps. There are other products out there, but these are the ones I have used. As far as PRE-emergent products Dimension is very good.
Late fall is still the best time to c ontrol most tough broadleaf weeds. Ground Ivy (Creeping Charly) responds very well to Trimec and other similar products in the late fall. These products can be used in much cooler temperatures than what has been reccommended. After the first killing frost, these products work very well. We have used them as late as Thanksgiving with very good results.
I agree as well with dougaustreim. Fall is also a great time and sometimes the best time to control weeds. But if a customer calls you in May and wants his dandelions sprayed, I would doubt he would be willing to wait for the fall to spray.
Haven't used Drive in the PG simply becuase it settles outr so much that it requires some decent agitation to keep it suspended for application. Best way for us to spray have been with the 2gl. hand held docs and the solo backpack.