I have been an expert at S-35 protein labeling during my PhD.
It depends what you want to do. Do you want to assess the synthesis rate or degradation rate of a protein?
To assess synthesis rates of proteins, you pulse (add a small amount of S-35 methionine) and then wait 2-30 minutes depending on the size of your protein.
Then you can lyse your cells after pulsing, immunoprecipitate and run them on a gel after the IP. This would give you synthesis.
If you are assessing degradation, you can pulse then wash cells after a set time and then chase to assess degradation. There are many research papers on this method, however its not well known.
If you need any help, ideas or just to let us know what you are doing just post back here, would love to hear from you.