Command not found when trying to set a format for the time command

This is because time is a bash builtin command - and the builtin doesn't support the options you're trying to use.

Try this, use the full path of time to skip the built-in and use the real one:

/usr/bin/time -f "%E" ls -l

Unfortunately, time is both a bash keyword and a program in /usr/bin. If you specify the full path to time, as in /usr/bin/time -f "%E" ls -l you will get the output you were expecting.