How long an aftermarket clear coat lasts depends on many factors: What clear coat was used, how was the surface it was sprayed over prepared, how was it sprayed (most important factors being how closely were the mix ratios and flash and cure times followed per Technical Data Sheets), and lastly how was it maintained over an extended period of time.
What aftermarket does have going for it is that because of application techniques, it tends to have a thicker film build.
There are aftermarket clear coats out there that reach full working hardness within an hour @ 65deg F. There are also clears that even after a 30min bake @ 150deg F ambient booth temperature still take up to another 24 hrs or more to reach that full working hardness.
By full working hardness, I am taking about the paint being cured just enough to the point that a technician can put there hands on the vehicle and do reassembly work. All-in-all it still takes around 30 days for a clear coat to reach its full cure and hardness all the way through.
Also, what color was sprayed underneath is another large factor.