That feature is not in Thunderbird, and I doubt there is an addon for that. You might try updating settings to not check mail and then do it manually when desired, although users have reported difficulty in preventing the default automatic checking for POP accounts. And I don't think it's possible for IMAP accounts, but that may vary, depending on the email provider. Good luck.

Hello David, Thank-you for the very quick reply! Having to manually stop checking emails, then having to start again is what I've been doing & got fed up with it, hence hoping it might be possible automatically. It's a great shame that feature is not available in TB & it should be, maybe programmers will decide likewise...

"Actions always speak louder than words"