I'm wondering who people use for a reliable late night SP.
While it seems like if there is a demand, there ought to be a supply, one also has to consider the other side of the coin.
SPs that enjoy what they are doing and are leading reasonably balanced work/home lives do not like to take last minute calls, period. Regardless of the time of day. Getting a last-minute reply during the day, from someone that is good at what they do is unlikely. So, consider that the SPs that are replying are pretty desperate for work, and probably aren't that good at what they do. Throw into that, 1am, and now it's even less likely to find quality or, as you asked for, "reliability".
It's not an answer that you want; and there are no doubt some SPs that prefer working late at nite (because they are nite-owls, because they have day-jobs, because they have families, etc.) who are good, given the size of the Ottawa market, it's less likely here than in a bigger place like Toronto or New York...
The final part of the other side of the coin is: for those who do work at night, what is the demand like? Who are the clients? Many of them are drunk. Risk is higher. While there are some travelling perfectly safe business people who have just gotten in from that 6h-long sales event and need to wind down, can you make your entire business model on this? So as an SP, one has to ask when then market of lowest risk, higher value clients?
Personally, I would love to be able to SMS someone at 7am for an 8:30am appointment. On the bus route to work.