Unfortunately, the SFMTA is in the process of moving their schedules around between websites and either they or the MTC have made an utter mess of the process.
That said, the information is still out there:
The F-line [streetcars] is open 365 days a year from before 6:00 a.m. until after 1
a.m. Streetcars are scheduled to run at least every 15 minutes and as
frequently as every six minutes during daylight hours.
The cable car lines operate 365 days a year from 6:30 a.m. until just
after midnight. Cable cars are scheduled to operate every 6-15
minutes, depending on the time of day.
As with all SFMTA services, there's no real point in trying to show up at an exact scheduled time. The bus drivers won't bother, except at terminals sometimes, so you shouldn't either. Your best bet is to use the nextbus.com service (or an app like Transit, which uses the same data) for realtime GPS predictions and a live updated map. Note that this data is sometimes inaccurate. The F-Market streetcars are listed, and you can scroll down to the bottom of the route list for the cable cars.
The F-Market streetcars do have a schedule, though it's more of a aspiration than a useful document. You can find it by going to this page and choose F (or E, for streetcars that continue around the Embarcadero). Choose between inbound/outbound directions and the day of the week.
If you need live transit help in San Francisco for questions like this, you can dial 511 (or 888-500-4636 if you're not in the area). To talk to a live person:
Just call 511 and ask for "Transit Agencies" and select the
appropriate agency. Once you select the agency you want, you can
choose to be transferred to that agency from the list of options. For
example, saying "Operator" at the AC Transit menu will result in a
transfer to an AC Transit operator who can assist you with AC Transit
schedules and trip planning. Please be advised that pressing "0" on
the system will NOT connect you to an operator.
511.org also has a trip planner that searches schedules, or just use Google Maps.