Your help is highly appreciated.

in 3 column next to each other in each cell I have a drop down list for a
user to pick up a value from e.g. 1:00, 2:00, 3:00

how can I restrict the user as such; if value in cell A1 is greater than 1
then value in cell B1 and C1 must be 0.

and if the value in C1 is greater than 1 then A1 and B1 must be 0.

Please remember I already have data validation as a form of LIST configured.