Return a Float that represents the time value of {time}. Example:

let start = reltime()
call MyFunction()
let seconds = reltimefloat(reltime(start))

See the note of reltimestr() about overhead. Also see profiling. If there is an error 0.0 is returned in legacy script, in Vim9 script an error is given.

Can also be used as a method:

reltime(start)->reltimefloat()

only available when compiled with the +reltime feature