Yep, there is no VR required on alternate fuel in IREX anymore (VR is calculated on the trip fuel only, and only for RPT/CHTR), so the latest divert time in your example is now i.e. 1300
Be careful as the alternate may have its own holding requirement due weather, lighting or traffic - all of which would make the latest divert time earlier.
This isn’t a well constructed question as the fuel on board minus the FR exactly equals the flight time to the alternate. Normally the questions in the IREX would have a latest divert time sometime after the initial conditions are given.
To your point though, yes, it’s latest divert time and in IREX there’s no requirement to include time for approaches at the destination or alternate. So start with the required fuel on board arriving at the alternate (any holding plus FR), add the flight time to the alternate, then subtract the result from the current fuel on board. The result is how long you can hold at the destination before diverting.