Just some back of the napkin notes if the volcano went large and created a tsunami threatening the Atlantic seaboards.
Looks like the Canadian maritimes (2,200 mi) and NE South American coastlines (2,600 mi) would be first hit in the western hemisphere.
Using an average depth for the North Atlantic of 12,880' and standard inputs for gravity and density you get a computed tsunmai speed of 438.91 mph.
I've seen data buoys go off sooner and later than calculated, so this is a rough estimate.
Rounding up to 440 mph provides the following guestimates for event-to-impact times:
Canadian maritimes: 2,200 mi / 5.0 hours
Eastern So. America: 2.600 mi / 5.9 hours
New England/Eastern Caribbean: 3,000 mi / 6.8 hours
Mid Atlantic/Chesapeake Bay: 3,400 mi / 7.7 hours
Florida east coast: 3,777 mi / 8.5 hours