The first coat usually goes in the roughest area and the filler is built out from there. You can really save some time and effort by starting the sanding slightly early while the filler is still a bit soft. Just be sure and keep a blow-gun handy to blow out the sand paper frequently. The best grit I’ve found to rough-in large areas like this is 24. It’s fast but there are some tearing issues like shown in the second picture. There are also ways to be efficient while the filler is drying completely. I used that time to grind the top of the quarter panel for filling and I added some more fiber hair filler to the rust pits at the top seam and the wheel house.
What has been done so far took about 3-3.5 hours of shop time. I think I only billed out 2.25 hours though. There are always breaks in the work as well as phone calls, other distractions, and of course there’s time out to take pictures. All this work was done yesterday and the shop should be warmed up to working temperature by now this morning. Thanks for reading. -Kevin