Finding key in array-valued dictionary by giving an element of array. (CSP)

Question

I am trying to solve a constraint satisfaction problem with python. There are 4 people going to a party at 4 different times.

timeDomain = {"4:30" : ["brian", "amber", "chris", "diane"],
              "4:35" : ["brian", "amber", "chris", "diane"],
              "4:40" : ["brian", "amber", "chris", "diane"],
              "4:45" : ["brian", "amber", "chris", "diane"]}

The constraint is "amber comes 5 mins before brian". So, how do I compare brian's and amber's times with this dictionary? I want to write the constraint as a boolean variable named c:

c = ambers time == brians time - 5

(with converting the string values of the minutes to int etc..)

I tried

list(timeDomain.keys())[list(timeDomain.values()).index(["brian", "amber", "chris", "diane"])[1]]

to find amber's key but it is not working because all the values are the same, I guess.