How far after the fact can late fees on late rent be charged and collected?

There is not a law, per se, that says when a landlord has to impose certain fees... however, you may have a couple of options for relief.  The first is your contract.  If your lease agreement places limitations on when and how, then you can invoke that remedy.  The second is to review any local Rent Stabilization Ordinances (or RSO's).  There are local codes that are somewhat unique to California and a couple of other states.  They can place limits or restrictions on when/how landlords impose rent requirements and associated fees.  These are very important because they cannot be contractually waived--- meaning that if the RSO limits how/when late fees can be imposed, it doesn't matter what your lease says.  Your third option is to tell your landlord that you simply aren't going to pay them.  After a California Supreme Court Opinion in 2004 ( Orozco v. Casimiro, 121 Cal. App. 4th Supp. 7), it became questionable whether or not a landlord could even impose a late fee, and if so, placed limitations on the practice.  Considering that it's taken them almost a year to be bothered by it, your landlord is going to have some problems if he tries to take you to court to collect.   If you want to use this opion, just send him a letter advising him that you think the fees are unreasonable in timing and amount, and you are requesting a waiver pursuant to the opinion noted above.  Just know that if you do this, that it could result in an eviction suit.  If a legal aid organization is not willing to represent you (as was done in this case), you would have to pay an attorney out of your own pocket, which could be more expensive than just paying the late fees.