When I started I offered 24/7 care. This area is tough to get clients, so I had to start with something and we also did not have our son yet. A&B is right you are more aware of others kids in your home and it's hard to rest well. One of the kids that stayed sometimes overnight was a 5mo boy. When he came I would sleep besides him. I was so afraid of SIDS (I know, there is nothing I could do about if SIDS happened) but anyways I felt like I have to keep a close eye on him. So I woke up several times to check on him. I also had a 3yo girl that jumped the upper stairs gate (nap bedroom is upstairs) to go downstairs to the play area before I woke up. I do not know how she did not hurt herself. She was happily playing when I woke up... Also, as Judy mentioned most parents want to pay less because their kids are supposed to be sleeping and you technically are not doing much other than laying in bed... This service is not valued en enough and there is too much liability.
If I ever have to do it again I will charge per hour and it will the highest rate that a experienced nanny charge in this area.