I desoldered tenths of BNC connectors from PCBs by keeping outer part of the connector (edge) slightly pushed against surface of heating platform set to 290 to 300 degrees Celsius. Then soldered to other PCBs. Temperature may depend on solder used. Although contact area was very small (thin circular edge), it heated up within minute or two and went out very smoothly, sometimes I needed to pull BNC connector with tweezers to heating platform direction, and PCB to opposite direction. Plastic material inside connectors not melted, but I often do small repairs and resoldering, so can't guarantee on this. I think connectors probably must withstand 260 deg short term, not sure. I have used this heating platform, but a smaller size (image in attachment). I am sure that with heating gun I would damage PCB, because too much hot air moves around compared to heating platform.
Moreover, I've bought new BNC connectors for repairs few times, and struggled of soldering them for a long time (flux, grinding, 300+ Celsius soldering iron). All problems was gone after using heating platform: I set it to around 200 deg, put all BNCs upsidedown, preheated, and accurately placed PCBs on top of them, so BNC four ground pins and one signal pins inserted in PCB dedicated holes, and used 290 deg soldering iron to solder them one by one while keeping BNC edge pushed against preheating platform. But there was another problem, some LEDs weakly lit up when soldered signal pin of BNC, so there was some ac or dc present between platform and soldering iron, which is not good, and must be careful. Everything worked after repair though.