Are the New Haven taco trucks there on Sundays?
Trucks are there 9:30am-9pm, 7 days a week.
That's the answer I got after calling Ixtapa Grill (203-230-2586), a restaurant in Hamden, CT, which runs two of the many trucks on Long Wharf.
The guy on the phone said the times are approximate. In my experience you're within an hour on either end, they're there.