Dictation on my MacBook Air/Catalina

I'm finding that if I take a break from dictating for awhile, even if the microphone icon is still on my screen I have to go back into Preferences/Accessibility/Voice Control to reset it. Is there any way to keep it active or does it automatically turn off?

ALSO: Even though my diction is very careful and I don't have background noise, there are many, many inaccuracies in the transcripts. Would using a plug-in microphone yield better results? If so, which microphones would you recommend for that are compatible with the MacBook Air 2020?