Sorry your having such a hard time on the wafers sticking, hang in there everything has a learning curve and we're all here to help and trade tricks we learn.
My process is lay out your stuff before hand, the cold weather is here and warming up the paste, wafer, and anything else that needs to be sticky. I use a heating pad on the lowest setting and place things on top when I am in the shower so the glue is sticky.
A good shower and cleaning of the area with soap without moisturizer for the area is a good start. Remove everything to get a good cleaning and gentle clean the area but do not rub to hard. You do not want to irritate the skin.
Let the area dry out and if possible breath before putting on application works great. Start with adhesive remover to clean off any residue and the wipe with wet paper towel to clean off the remover chemical. Next a barrier prep wipe is applied to make the area sticky, let it dry.
My trick is to place the ring barrier around my stoma on the skin and put the paste around the opening on the wafer hole sticky side then put it on.
The surgeon had a friend he worked on and he shared his trick. Only works on 2 piece systems. Buy a pvc pipe fitting, must be round. Mine is a 1 inch to 1-1/4 adapter. I press it over my stoma with the opening allow my stoma on the inside of it, the sides of the fitting press inside the flang of the wafer and push the barrier ring into the paste. The paste will squeeze though the voids in the opening of the wafer and your stoma sealing it up and bonding them together and against your skin right up to the edge of your stoma where leaks start and failures occur. The fitting will pull away any excess paste. Add half moon rings to the wafer on the sides for added security. Finish up the rest of the process from there.
Most I have heard some have gone from 2 - 5 days on the wafer. I replace the bag 2-3 days because of the filter getting wet and failing but have got up to 10 days on the wafer without a failure. That is pushing the limits of the adhesive because the bond will break down over time from sweat and dry out which can cause failure. Would not recommend that length of time for skin health but it is possible if your short on supplies. High watery output can shorten the duration of changes also.
Winter time is normally when I have seen people having the most issues.
Hope this helps