I have assisted the vet when it was spay day for SBR and the insision for that is not stitched up.. We shaved things but it wasn't noticable when the job was done.. Just watch it if it has you worried and if it looks odd in any way, call the vet..

My vets always let me pick them up the same day... provided it was done early in the day.. Maybe that vet didn't get to it until late in the day and that's why he had to stay overnight.