Actually, to make it clearer, won't use now() in the function:
? datediff("n", #7/apr/2019 23:00#, #8/apr/2019 01:00#)
120
As an aside, if I had of entered the date as '8/4/2019' the system assumes it's a US date, again, a pain in the a..... always catches me out.
You can use only the...