Each supplement stack is designed to last 1 month, but some of the individual products may last slightly longer (such as PSI, RP Max and OxyShred).
It depends on how often you use the products:
For example, OxyShred can be taken 1-2 times a day. It has 60 servings so if you have it in the morning on an empty stomach as advised - it will last 60 days :) However, it can be used as a pre-workout too so on the days you workout you can take another serving of OxyShred which will decrease the time that the OxyShred lasts.
OxyWhey is 30 servings and if you use it every day (because it tastes amazing) it'll last one month - but some people only use it on the days they workout (post-workout snack) which will increase the time that OxyWhey lasts.