You need now(), not today().
Now() returns a number with a fractional part. The integer part is the current date (the number of days since 1900 Jan 1st), and the fractional part is the current time. 1 day = 24 hours. Therefore 1 hour = 1/24.
4pm is 16/24 = 0.6666666666666667
Therefore, to check if the current time > 4pm you can use the following expression:
let time = now()
(time - floor(time)) > 16/24