There's no native function to parse a string into a time. The other direction is possible, though, because the
strftime() function you mentioned takes an optional second parameter,
:echo strftime("%Y %b %d %X", localtime())
2019 Feb 20 12:12:12
The form of the time is seconds since epoch (1/1/1970).
localtime() returns current time in that form which is why I used it in the example.
By the way,
strftime() isn't portable. It's system dependent both in it's presence or lack there of as well as determining what are valid format strings if it is present.
Since portability is out the window might as well use external commands (e.g.
:!date ... if you're on *nix). :)