The maximum time step in Explicit Dynamics is calculated using the minimum characteristic length of all the elements in the mesh. In the Mesh Details, request the Mesh Metric of Characteristic Length (it is the last item on the list so scroll to the bottom of the list).  Look at the statistics on this metric. If the average element length is 100 mm and the minimum length is 1 mm, it is the 1 mm element that sets the maximum time step. Look at where the 1 mm element is. Simplify the geometry so that it can mesh with a larger element. If you can remesh so the smallest Characteristic length is 10 mm, then the 300 hours will be reduced to 30 hours.  If you can get the minimum length to 100 mm, the solution time might reduce to 3 hours.

Under Analysis Settings, you can type in a larger Maximum Energy Error to keep the simulation running. After it finishes, you can plot the Energy Error and evaluate whether the simulation is acceptable.