Data Validation Formula

Hi, I need help with a data validation formula related to time.

The values involved are:

Regular Start Time (cell C1)
Alternative Start Time (cell C2)
Late Arrival Time (cell C3)

I want to have a data validation formula within (cell c3) whereby a time is only allowed there if it is late according to 2 simple rules.

Rule 1) If there is NO Alternative Start Time (ie C2 is blank), then the Late Arrival Time (c3) must be later than the Regular Start Time(c1)
Rule 2) If there IS an Alternative Start Time(AST) then the Late Arrival Time must be later than the AST irresepctive of the Regular Start Time.

Logically in my head this should be a fairly easy data validation formula, yet I am stumped at every attempt to solve it.

See simple screenshot below

time.PNG

Hey unfortunately that formula didn't work.

See attached file for testing.

Sorry see file attached here.

In the Data Validation dialog, uncheck the box that says "Ignore Blank"

ok solved. thank you very much. jus needed to deselect the ignore blank checkbox.