I want to perform the following Statements in Excel only on certain condition

NOTE: AN4 an AO4 cell format are Date short

I am doing the following:

Column BK:

=IF(AN4<AO4,"LATE","Ontime")

Very simple I agree BUT I want to execute that statement only when:

AN4 and AO4 are not empty

ALSO

If AN4 has a date but AO4 is Empty, I want to write in column BK: In Delivery

If AN4 & AO4 are Empty, I want to write in column BK: Order in Process