Excel 2007 : How to determine which cell is occupied and has least value?

I have to simulate bank transactions using excel. I've generated random numbers for the service time as well as the arrival time. The customer chooses the available server upon arrival. If all servers are occupied, the customer will wait in the shortest queue. Otherwise, if more than one server is available upon arrival, the customer chooses server 1 by default, then 2 and so on. The shortest queue is the earliest time of departure of the customer currently served by the servers. What would be the syntax for choosing which server the customer should go to? How do I determine which cell is occupied and how can i compare cells which are not exactly in order, to see which has the least value. I have attached the file for reference. please help.

I'd be inclined to insert a blank column between Arrival (H) and Server 1 Start such that the latter moves from Col I to Col J and Col I is blank - at which point:

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then copy J6:K362 and paste to L6:Q362

I would also revise the Waiting Time calculation (Col R post column insert)

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edit: figured I should add a working sample as proof of concept