The empeg can check the signal strength quickly (a few milliseconds), which is what it uses to poll AFs.

However, to pick up the PID (16-bit station ident code) from RDS requires - with 100% RDS reception - up to 104+103 bit times (104 bits is a packet, assuming the worst case of coming in one bit too late). At 1187bps, this is about 174ms.

In actual fact, you may need to wait a little to get everything settled; say 250ms. The empeg should be tuning to the wrong station for no longer than half a second before switching back - though I'm not sure if it "blacklists" AFs that it's found no PID on (it really should do this for a period of time like an hour or so).

Really high end RDS radios have twin tuners, allowing them to verify AFs before switching to them totally seamlessly.

Hugo