No.
Bacs payments work on a 3 day cycle.
Day 1 - data upload from your employer/benefit office etc
Day 2 - the data is visible in the system and the receiving bank can see the payment data due
Day 3 - is the normal payday
Day 2 is where Monzo and Revolut and other banks can see the data is due to go into your account, and Monzo and Revolut allow access to this payment evening time of day 2, as it’s unlikely the payment can be recalled after 4pm onwards.
Some employers will say paid by bacs on your payslip, but sometimes it’s faster payments instead (just like me sending you a bank payment).
If, at the top of your transaction feed it has a greyed out section of employer name and then amount, you can usually collect this around 4pm.
If this isn’t showing, your employer didn’t send the funds via bacs, but instead faster payment, which monzo can’t advance early because it can’t see the payment is due in to your account, these happen instantly.