How I can subtract minutes to format NOW?

[#1]

I need to subtract 30 minutes to the current time to determine if information entered during each 30 minutes.

Thanks for your help.

[Gysbert_Wassenaar]

time(now() - 1/48,'hh:mm') will subtract 30 minutes, 1/48th part of a day, from now() and show it in hh:mm format

[tresesco]

try:

timestamp(now()-time#(30,'mm'))

or,

Timestamp(now()-30/24/60)   // 1 means a day, hence 30 mins=30(1/24/60), or directly 1/48

[Logistix]

Excuse me, I need to do the same thing but this time, I need to subtract 10 minutes to the current date. Considering your answer, I think It'd be something like this:  

Now()-10/24/60

 The thing is I don't understand the process. Can you explain it deeper?

I don't really get why i need to divide 30, 24 and 60.