If your glue is "goopy" there's something wrong... NRS instructions may be geared to on-river patching, where you need the patch to stick and get you home. If it's below 50 degrees, humid or raining, accelerator is a good idea. If you're patching in a controlled environment, temp is between 60 and 80, low humidity, and don't need to float the boat in the next 24/48 hours, I see no reason to use accelerator. What's the evidence for accelerator producing a stronger bond? It's the underlying glue that creates the bond, it's called "accelerator" because the stuff makes the glue cure faster - not necessarily stronger...
Glue: should be free of lumps and "clear" when it runs off your brush (by "clear" I mean you can see through it, or when you apply the underlying fabric color shows through). Thicker than water, thinner than pancake batter. If you're going to err, err on the side of thin - particularly if temperatures are in the 80+/90 degree range. I have never used glue straight from the can without thinning, either PVC or hypalon.
10-15% minimum thinning, often need to go to 25-33%, sometimes even almost 50-50.
Several - many - thin coats are better than one or two thicker ones. And yes, if you don't mix immediately when adding accelerator - stir as you add for best results - then the stuff will react with the top layer of glue and you're going goopey...
Prep is 90% of the job. Abraded surface but not fabric, wiped with appropriate solvent (MEK for PVC, toluene for hypalon/Pennel), CLEAN and ready for patch to lay flat (or as flat as possible if doing V-tape, valve replacement, etc.) will yield best results.
Cure time and time between coats: dry is dry. If you let first coat dry so it doesn't stick to your finger, (i.e., "tack-free") you can then apply second coat. That might be 5-10 minutes @ 90 degrees, or half an hour at cooler temps/more humidity. If your first coat isn't dry in 30 minutes, likely your glue is too thick or you're trying under "inclement conditions" (cold, rain, etc.).
l like 3 coats, 4 if really going for something tricky, but seen some good patches laid down with just two. Advice above about laying patch and rolling out bubbles (you don't need a fancy roller, either, although NRS happy to sell you one - full beer can or any solid cylinder, even the handle end of your brush if nothing else available will work) is good. Think of your patch/D-ring and glue job as contact cement - where you lay it is where you end up. If you have to "do over" you have a mess on your hands and will spend twice the time cleaning instead of doing it right the first time...
Cure time: it helps to inflate the tube where your patch/D-ring is going after it's applied, just enough pressure to maintain shape. After a few hours, check it and change air if a big repair (once did a 30" tear in J-rig overnight... changed air twice and it held air remainder of trip). Don't inflate to full pressure for at least 12 hours, longer if you can avoid it, and by "full" I mean Udisco soft (1-1.5 psi). After 48 hours and a couple of air changes, if you did it correctly your repair should be good to go up to full pressure (2-2.5 psi).
There's lots more - that's why the pro glue-sniffers are in business - but above has worked for me for 40+ years and dozens of repairs and D-rings, pontoon builds, etc.
Laid my first patches with Barge, if that's any barometer... glues are WAY better today.
P.S. - heat gun is your friend, but easier to manage lifting old patches/glue (seam tape) than to reactivate new glue. Slow and far away (I use 750 watt setting, my $10 Harbor Freight gun has two just two settings, 750 and 1500...) and use a spatula or putty knife - carefully! - and you can lift just about any factory glued fabric. Welded is another story... also Dremel with 150 grit roller is great tool for roughing fabric asap. Obviously not available on river - unless you carry a generator (motor heads!) - but you're only as good as your tool...