How long does does an employer have to provide me with a W2C and can I file before I receive it?

My original W2 had an error in Box 12-W that showed me as overcontributing to my HSA. I am in the process of getting this resolved with my employer but they are telling me that it will take 12 - 18 weeks to receive my W2C.

That seems like a really long time, is that normal, or even allowed?

They are offering to calculate and provide me the correct numbers. Am I allowed to file with the correct numbers before I receive my W2C?

 

Thanks!