I am cooking a tator tot casserole and it has raw cut up chkn breast and frozen broccoli and frozen tataor tots . Can I cook it on high and my slow cooker as opposed to low to accommodate timer restrictions?
You'll be fine cooking on high. I'd expect it to be best at 50-70% of the time on low. Starting any significant ingredients from frozen, I'd be inclined to use high (or auto, though I've never had one with that mode) anyway, as the contents will take a long time to get up to temperature otherwise.
While plenty of things can't be cooked on low for safety reasons, there's very little that's improved by cooking low. Casseroles aren't among them
My slow cooker has generic instructions for timings as well as specifics for detailed recipes.
We don't know if yours is the same, but as a general guide…
Low 8-10 hours
Medium 5-7 hours
High 4-6 hours.
These timings assume you have pre-seared any meat.
Without pre-heating, add time… Low 2-3 hours, med 1-2 hours, high 1 hour.
It also says to add 15 minutes for every time you lift the lid, to stir etc.
Many of the specific recipes, though, give huge time variants for each dish - for instance goulash 4 - 8 hours on medium, chicken paprika 4 - 7 hours, med.
That's a lot of leeway in which you have to use your own judgement. For stewing/braising beef, longer is better, for chicken breast the shorter end of the timescale might be best. You may end up using the broccoli as your timer; it's done somewhere between when the broccoli is soft but not yet falling apart. Chicken breast somewhere between when the centre of the largest piece is no longer pink & it turning to rubber.
All of this is highly dependent on how full the pan is too. More stew, longer time.
You could reduce all these times if you bring your stew to a boil before putting in the slow cooker - but that's dependent on what your pot is made of. Mine is metal, so it goes straight from stove top to slow cooker. Also how easy it is to stir your stew. Tater tots don't strike me as being very stirrable; I'm assuming they need to just sit gently on top.