Uber is open all the time. If you are in an area where Uber is supported, you can usually bet there is one at all times of the day. I live in the suburbs, and at night, I see less cars, but there are always a few at all hours. For all I know, it could be some dude sleeping at his house who has the driver app on.
Basic supply and demand. The more drivers in the area, the more ability to fill the demand. If there are less drivers, which at night there are (and really early in the morning), then the demand may be higher than the supply of drivers.
Uber and LYFT platforms or apps, are utilized by rideshare drivers at any time day or night. It depends on a drivers desire to go out in public and drive. As long as there are enough drivers in the area (like if you're not in a rural area) there should be an active driver at all hours of the day and night, yes.
No the normal Uber rates are the same any hour of the day, unless of course your area is in a surge. Surge is basically supply vs. demand. If there are more request for rides than their are available Uber drivers nearby, the price goes up.
You can pay for rides by cash or card. To pay for rides by card, first add the card in the app. You can add up to 5 cards. Card payments are available for rides in the iOS (version 8.0 or higher) or Android (version 4.0 or higher) app.
When riders consider Uber, it's often as a one-time transportation solution. They might use it on vacation to get from the airport to the hotel, for instance, or to head downtown on a weekend. But there's lots of ways that Uber can be used on a daily basis, whether it's to commute to work or to pick up groceries.
LYFT's reliability at 4 am may vary depending on your location and local demand. It's generally a less busy time, so availability might be lower compared to peak hours, but LYFT should still be operational. It's a good idea to check the app closer to the time you need a ride to gauge availability in your area.