There's merit either way.
Integer.MAX_VALUE in milliseconds is a little more than 24 days. I doubt you would ever run into a query that would actually take that long and still have enough resources to actually finish, so an int has plenty of capacity to handle QTime. The difference is tiny for a single value, but a long does take up twice as much memory. If most of the existing code uses an int, I am inclined to stick with that and change the deviating code.
On the other hand ... everything else related to time in Java is represented as a long, as Anurag Sharma mentioned. If the value is ever used for calculation with any of those other numbers, it might save a tiny bit of CPU time if Java doesn't have to convert.
Switching everything to a long is likely to involve quite a bit of effort to locate and change every place that it's used, which is a big part of why I suggest sticking with int. I don't think we would ever need a long for relative times.