Gina - here is a simpler explanation
If you double a recipe, time and pressure do not change, IF you use the same mold that you used for the smaller batch. However, if you use a larger mold, then yes you need to increase pressure. Time stays the same regardless. As the size of a mold increases, the weight that you are pressing with spreads out over a larger surface area so you have to compensate for that. There are 2 distinct schools of thought among cheesemakers here on the forum.
The first is the "Big Rock" approach. Basically you try different size rocks (weights) like ancient cheesemakers until you find what works for you. If you are happy with the results, then you use that same rock (weight) all the time.
The other approach is more scientific and predictable using pounds per square inch (psi). Just search the forum and you will find several
lively discussions.