Hi Mike --
It is probably a little bit of both your possibilities. As Carol already stated, anything with nerve compression takes a while to recover from. Some people wake up from this procedure and the pain is gone, but for others, it takes awhile. Don't be alarmed. Just follow your surgeon's instructions for post-surgical care and you should do fine.
Being a fellow L5-S1 sufferer, I can assure you that it is very typical to have pain in the glutes, hips and buttocks after any procedure at this level. Everything is so closely related...when there is inflammation, it can cause the piriformis muscle to tighten, which can cause pressure on the sciatic nerve and it can pull taut, affecting the hip flexors, which results in what feels like "hip" pain.....
Since you say the pain gets worse at night, it may be that you are doing too much during the day, which is causing some inflammation. As the day goes on, the nerve gets more irritated. You might try resting a bit more to see if that helps.
Just remeraber that recovery takes awhile. Try to be patient and maintain a positive attitude. If things take a turn for the worse, call your surgeon...but, chances are, you'll be fine. Good luck.