Hi! I do only daytime work, and not even later in the afternoons, due to my own family's needs, and I get plenty of work. Not full time, but I don't want full time. I have a few overnight doulas who I refer to if the client is interested in that. I put my usual hours on my website, so most of the time people see that and only contact me if it falls within their needs.
There isn't a "usual" day, really. It can vary from someone who needs more physical, hands-on help around the house and with the baby (complicated BF situation with pumping, washing pump parts, preparing bottles, SNS, housework) and needs several hours, several times a week, or, more frequently for me, are people who need a few consultations for emotional support, talking about a traumatic birth, breastfeeding support, normal infant behavior and sleep concerns, demonstrating different baby carriers, helping them find mom's groups, lactation consultants, etc.
Since I like part time, and the consultation type clients, and doing breastfeeding support mainly, word of mouth spreads and that is mostly what I get. If you tend to work with people who want daily or full day support, that spreads in their circle and you tend to get that kind of work.
It also depends on how you structure your payment- since I don't want a ton of hours, I only have them pay per hour, as needed, so if they just want me to come for one 2-hr breastfeeding visit that's fine. Some doulas have clients purchase, 10, 20, 40 hours ahead of time so they can anticipate their work hours/income. Etiher can work- it just depends on how much you need/want to work and earn.