Registar-to-registar
The 60-day waiting period is usually only for Registrar to Registrar transfers.
If you want to sell the domain, you can push the domain to the buyers account (on the same registrar), wait the 60 days, or change the WHOIS info. However, I don't recommend just changing WHOIS info to transfer ownership of a domain, as personnel information might still be tied to the account at the register. For example: Credit card info used to purchase the domain!!
Hope I helped.
--UpSideDownKiwi