no one can stay online for 24 hours. staying online often is good as a result you can respond to your clients fast but spending too much time in the computer is not good. you can use this time to sharpen your skills instead.
yes, you can but the Best and ideal way to promote on Fiverr is through Fiverr's organic search results. Your gigs should be rich & compelling enough to reach potential buyers; and have the potential to elicit inquiries/orders.