For a small second degree burn that happened 3 hours ago, do i need to put silvadene (silver sulfadiazine) cream on it? is it available over the counter?

No: I don't know what you define as "small" or where the burn is. But, second degree burn means there is a blister. It can be treated by applying any topical antibiotic, like bacitracin, twice a day, and keeping it covered until healed. Bacitracin is over the counter. There is nothing magical about silvadene (silver sulfadiazine).

Second degree burn: The biggest risk for 2nd degree burns are infection and scarring. Silvadene (silver sulfadiazine) is by prescription only. You should apply an ointment during healing (bacitracin or similar antibiotic ointment) and apply a clean dressing daily. You should see your doctor as soon as you can to evaluate the wound, as some deeper second degree burns require surgery (e.g. Skin grafting).

Probably not: If the skin is intact there is no need to apply silvadene (silver sulfadiazine) cream. It is not over the counter. You can use regenecare to keep things moist then cover with a secondary dressing. Check your tetanus status.

Protect it: An unpopped blister represents a closed sterile environment. Yes on occasion one can become infected then it is time to open it, however the risk of infection in a dressed open wound is still higher than that of an intact blister. The blister will gradually resolve with time i wouldn't use an ointment on blisters at all silva dine no help now.