Sorry, I meant 301. The title is a typo
302 is a temporary redirect, so you leave it as long as necessary - until the temporary situation changes.
301 is a permanent redirect. If your page has changed permanently, then you want to leave the redirect there permanently, so that any incoming links from other sites that point to the old page are automatically redirected to the correct new page. As your site was only online for a month, you may not have any links to your .htm pages, or they may be so few that you can contact the relevant sites and ask them to update their links. In that case, you could probably safely remove the redirect once you're sure Google and the other search engines have updated their links. Personally, I'd just leave it permanently. Having it there if it's not needed won't cause any problems; not having it there if it is needed might. :)
Excellent, makes perfect sense. Thank you!