Don't think Timmy would survive against a top 20 boxer under boxing rules.
Two things to consider is we have never seen Timmy fight with boxing gloves, it is a lot easier to block a punch with the big gloves and it is also a lot easier to block a punch and throw a punch when you don't have to worry about being kicked or taken down. That being said, I still think Timmy would be a punching bag for any decent heavy weight.
On a somewhat unrelated topic, did anyone watch the Klitschko\Thompson fight last night? For the first 5 or so rounds, Larry Merchant was so negative about Klitschko, making him sound like this glass jawed looser, how many years ago was the Sander's fight?
Also, not that it was too bad last night, but they should do more about the clinching in boxing. They should treat it like grabbing the cage in the UFC, clinch once, get a warning, clinch a second time, have a point deducted, it would make boxing a lot more exciting. The two punch, grab the guy and wait the for the ref to break up the hug isn’t great to watch.