What is the timestamp url?
The timestamp url will mark your file with a date and time that it was signed. This guarantees that your digital signature will remain valid even after your certificate expires. Although there are some CAs that do not offer certificates that can be time stamped. Or their validity will still expire.
Comodo's url is http://timestamp.comodoca.com/authenticode
Verisign's url is http://timestamp.verisign.com/scripts/timstamp.dll Note the lack of an e in the dll
Thawte's url appears to be the same as Verisign's.
You can use any timestamping url regardless of your certificate's origin.
For SHA256 timestamping, use globalsign with the signature=sha2 parameter. The other 256 timestamps do not seem to function correctly with even signtool. Or when I was testing, they were having a bad day. Comodo's worked once out of ten tries. It kept signing with the SHA1 default. And the other one I found didn't even stamp it with anything.