One common thing is that the radio needs time for it's clock source to stabilize. To make them cheaper they usually use things like phase locked loops to take

One common thing is that the radio needs time for it's clock source to stabilize. To make them cheaper they usually use things like phase locked loops to take a lower frequency clock and multiply it up to the clock they need. This can take tens to thousands of milliseconds to bnot be bouncing around when first configuring the loop. And with modern radios, these loops get programed at run-time from the firmware because they need to be at a large range of frequencies. During this startup you can't transmit anything, because you'll transmit with another signal (the clock jitter) mixed in which adds noise, at best, and possibly even at a completely incorrect frequency which will result in fines or possibly jail time. The safe route is just to wait instead. Receivers work similarly, using PLLs to downmix the signal they want, generally, and while they can begin trying to receive while waiting on it to stabilize, it's usually pointless because you'll just be getting unintelligible garbage from the noise or wrong frequency.