It will be tight but if all you want to do is take in the view for 20 min you won't have a problem. If you take longer than 20 min then you'll be cutting it close.

Assuming you land at 11:35, you still have to go through immigration/customs. In an ideal situation, you'd be at the Airport station at 12:15. Assuming you time it correctly, you can take the Star Ferry from HK to Tsim Sha Tsui by 1 if you walk around a bit on the HK side. The Star Ferry is probably only a 5 minute ride these days after they moved the pier farther and farther out, shrinking Victoria Harbor. Walk around the pier/walk of stars and head to Jordan Station and hopefully back to HKG by 2-230.

Everything will be bang bang and leave you wishing you had a bit more time. If there are any delays though, you'll be sweating your next flight.