The answer to this question is: it depends, on a bunch of stuff!
Is the oil new? Has the new oil been pre-filtered? New oil is dirty oil, and if you have a high purity application, all new oil should be filtered prior to being added to the system.
If the oil in the system is dirty, the life of the elements will depend on how contaminated the oil is to start off with and how clean you need the oil to be. If a filtration system is installed when the oil is full of contaminants, you may have to change the filters more frequently at the beginning of the process. Once the filtration system removes the majority of the contaminants and your oil becomes cleaner, the length of time between filter changes will increase.