hours and hours of sanding is an understatement. thast the hardest part to take your time on and its the part that will show the most errors if u rush.
when i'm dealing with bondo i have a tool called a cheese grater and soon as the bondo starts hardening you use the cheese graer to get any high spots first so u save some sanding time. and them i do mine pretty much the same. sand it smooth, spray it with primer. sand and find the low and high spots, fill them in and redo the hole process till its smooth. for pinholes don't use bondo use glazing putty wich is the stuff elemental suggested. its much faster just plop some on your finger and smooth it over the hole. no mixing required.
when i'm dealing with bondo i have a tool called a cheese grater and soon as the bondo starts hardening you use the cheese graer to get any high spots first so u save some sanding time. and them i do mine pretty much the same. sand it smooth, spray it with primer. sand and find the low and high spots, fill them in and redo the hole process till its smooth. for pinholes don't use bondo use glazing putty wich is the stuff elemental suggested. its much faster just plop some on your finger and smooth it over the hole. no mixing required.