Hello 'chrystal_moon',
Many, many people wish they had more than 60 days in which to leave feedback,
particularly when a seller from a certain country on the other side of the world has
lied to them, delayed them past the resolution deadline, and stolen their money.
Alas, as you will see from the following link,
http://pages.ebay.ca/help/feedback/questions/leave.html
ebay thinks that is loads of time, as they assert, "you have a full 60 days to leave Feedback".
Not just 60 days, but a FULL 60 days.
You can, however, reply to any feedback that may have been left for you, or for those
occasions when you have left it and wish to add, you can do that indefinitely.
http://pages.ebay.ca/help/feedback/respond.html
If the prolonged interaction has gone as well as you say, even though you can no longer
leave feedback you can always send a kind note of sincere thanks to the seller. 