Specifically, there are responsible disclosure guidelines that came about to deal with the problem of people dropping 0day on a vendor with no prior warning. So the 90 days is a commonly-accepted amount of time to give a vendor to produce a fix. If the vendor needs more time they can request that the submitter give them an extension, although in this case it appears the vendor never responded, thus the repeated entries in the timeline saying "tried to contact vendor, no response" to show they tried to do the right thing.