If you have Supernatural you could have your vampire sim make many Invigorating and/or Potent Invigorating elixirs from the Alchemy skill and use those to stay up longer. (The Make Many Elixir mod from MTS really helps crank out elixirs, your sim will just have to grow the ingredients.)
I think the sauna from the Store also replenishes energy on using it, as does the massage table (which requires a 2nd sim to use).
Aside from mods, those are the only ways I can think of to stave off bedtime. There is no LTR for slower energy decay. There is an LTR for faster energy gain (Meditative Trance Sleep) and the Super Sleeper from the Store can replenish energy in 3-4 hrs.
