I'm setting up a new AP so that I can move some clients from a heavily loaded AP to the new AP. I wanted to test each client connection to make sure that it'll connect to the new AP before saving those settings. I tried it with a client SU by putting the router in safe mode (Ctrl-X in a terminal window) and then changed the SSID to the new AP and applied the settings. The problem I'm having is that safe mode restores the original settings in about 10 seconds because the client SU has been disconnected from the old AP. This doesn't allow enough time for the client SU to connect to the new AP.

I'm watching the new AP, and I don't see the client SU connect (even briefly before safe mode restores the old settings). Some of the references I have seen said that safe mode doesn't restore the settings until the default TCP timeout of 9 minutes. While 9 minutes is rather long, the 10 seconds or so that I'm seeing is too short to allow the SU to connect to the new AP. So, it doesn't seem that the references to a 9 minute timeout are correct.

Is there a way to adjust the safe mode timeout so that it leaves the settings in place for something like a minute or two (I'd even settle for the 9 minutes at this point)?

No, there is no way to adjust the safe mode timeout.
But you can write a script restoring the settings, and then scheduler running the script after 2 minutes from now, and then - just move to the new AP. If you are able to restore the connection with the new config - just log in and remove the scheduler and the script. If you're not able - after 2 minutes the device will be back .
That's one of the reasons why we love MikroTik scripts .

Thank you for letting me know. I was looking for the built in answer, but I can work with scripting it. I still think a configurable timeout on Safe Mode would be a useful feature (there are certainly those who don't have the ability to create scripts for this purpose).