It would probably not be a good idea to use clindamycin for more than 10 days at most. Clindamycin is a very strong antibiotic and very effect at killing bacteria in the oral cavity but it also can have a severe side effect because of its effectiveness. It can disturb the natural balance of bacteria in the intestine and can result in gastrointestinal problems such as severe diarrhea or psuedomembranous colitis.
You can attempt to delay treatment by taking the full course of antibiotics but you have to be aware of the risk of developing an abscess as well as potentially causing more damage to the tooth and jaw bone which may results in lost of the entire bridge. As with all abscesses, it can be life threatening and can have serious consequences. I would recommend seeking a more definitive and permanent solution for your problem rather than take a chance on antibiotic therapy alone.