Null Check in FX

Null Check in FX

Hi, 

Just created an overtime form for staff, but my Zoho is somewhat rusty after several years. 

Hours are calculated between a start date:time and end date:time:

"Minutes" <((End_Time - Start_Time)  /  (1000  *  60)).round(2)>

"Hours" <(((End_Time1 - Start_Time)  /  (1000  *  60)).round(2)  /  60).round(2)> 


From these Minutes, I calculate how many hours were worked and if the person is eligible for 1.5xpayment or 2xpayment. 

"Overtime 1.5" <((Minutes  -  450)  /  60).round(2)> 

"Overtime 2" <((Minutes  -  690)  /  60).round(2)> 


Now if the staff member has worked 10 hours, he is eligible to 2 hours at 150% but none at 200% but my overtime 2 returns -2

So I want to add conditional, that if extra time is below 450 minutes, then 'Overtime 2" = 0 


If I click conditional formula I get the following :

((Minutes  -  450)  /  60).round(2) if(input.Overtime_1_5 < 450,"0","0")

"Your expression is not valid, please check the syntax"


What is the valid way to conditional an FX field for a null check ( if(input.Overtime_1_5 < 450,"0","0")) AND do the FX calculation? ((Minutes  -  450)  /  60).round(2)


Thank you!