All the advice above is good. One further point though.
If you have several rolls to develop (say 6), and a tank that will require you to split them up over more than one run (say 3 batches with two rolls each), and you intend to develop all three batches, one after the other, on the same day, than with respect to the stop bath, you may as well re-use it as it certainly has extra capacity. If you get it near the end of its capacity the indicator in it will change the colour from yellow-orange to blue.
Relatively speaking it is really cheap, so I wouldn't store it and re-use it over several days.
And by the way, your fixer is of high quality and is easy to use and ship, but will require longer fixing times than the liquid Rapid Fixes. If you get a chance (at a photo store or through a good delivery option) to obtain Rapid Fix, it is worthwhile.