In case anyone else is following this thread...
Darwyn and I had a series of off-list emails that we think have resulted in the resolution of the problem. It appears that the problem resulted from some fields in the set definition for the gateway set being undefined. In particular, the fields timeInterval and versionsPerInterval (and there may be another) were being imported from a set definition file that left values for those parameters empty. Filling in those values appears to have resolved the problem.
WeBWorK Main Forum
Argument isn't numeric in localtime
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