### Subtract seconds from a time

You can subtract (or add) a number of seconds from a time using fractions.
Dates are represented as sequential whole numbers so 1 hour is equivalent to the fraction (1/24).
Times are represented as fractions based on there being 24 hours in a day.
1 Hour is 1/24 = 0.04166
1 Minute is 1/(24*60) = 1/1440
1 Second is 1/(24*60*60) = 1/86400

Cell "A1" displays the current date. Custom format "dddd dd mmmm yyyy".
Cell "A2" displays the current date and time. Custom format "dddd dd mmmm yyyy hh:mm:ss".
Cell "A3" displays the current time minus 200 seconds.
Cell "A4" displays the current time minus 200 seconds using the TIME function to return the correct decimal.
Cell "A5" displays the current time minus 40 minutes and 50 seconds.
Cell "A6" displays the current time minus 40 minutes and 50 seconds using the TIME function to return the correct decimal.
Cell "A7" displays the current time minus 3 hours, 15 minutes and 30 seconds.
Cell "A8" displays the current time minus 3 hours, 15 minutes and 30 seconds using the TIME function to return the correct decimal.
All these cells have been formatted with the custom number format "dddd, dd mmmm, yyyy hh:mm AM/PM".

 A 1 =TODAY() = Saturday 30 October 2021 2 =NOW() = Saturday 30 October 2021 08:55:54 3 =A2-(200*(1/86400)) = Saturday, 30 October, 2021 08:52 AM 4 =A2-TIME(0,0,200) = Saturday, 30 October, 2021 08:52 AM 5 =A2-(40/1440)-(50/86400) = Saturday, 30 October, 2021 08:15 AM 6 =A2-TIME(0,40,50) = Saturday, 30 October, 2021 08:15 AM 7 =A2-(3/24)-(15/1440)-(30/86400) = Saturday, 30 October, 2021 05:40 AM 8 =A2-TIME(3,15,30) = Saturday, 30 October, 2021 05:40 AM

#### Built-in Functions

NOW - The serial number of the current system date and time.
TIME - The time as a decimal given an hour, minute, second.
TODAY - The serial number representing today's date.