I know the
time command allows you to time the execution of a given command. But is it possible to get the execution time of the previous command without re-executing that previous command?
If you run around the block and don't measure the amount of time it took, didn't watch any clocks before, during or after and no people saw you do it, you also don't know how long it takes on average; would you be able to tell how long it took you to run around the block?
At best, you can know when you launched a certain application.
HISTTIMEFORMAT="%F %T " history
But that doesn't tell you when it has ended, which you will need to deduce, if at all possible.