Best countdown timer for comics?

Hi new to selling comics this week. I've been going through my boxes couple nights this week to get feel for things. Usually takes about 2-3 hours to go full box with some giveaways.

Count down time anywhere 15-30's but should I do faster 5-10sec... Sometimes I pre discuss before.

Should I put price sticker suggestions?

Group in $1, $5, $10 starts... Since new I know taken a hit on some titles and most have sold in $3 range but some I've started at $25 even a $150 key that has sold.

Most hit $3. Crazy bidding war on a title wouldn't even expected lol.

All in all been fun as a seller and easier than taking to post thousands of comics in eBay.

@njt3