Arcgis is sometimes slow. But it does the job. May be wait a little longer, the number of stops you have is a big number. Else check your connectivity before you run the tool.
300 meter is not too large and you should be able to generate the 2800 bus stops relatively quickly. Perhaps there is something else going on with the data. Have you tried running the service areas, 100 bus stops at a time? Maybe that will narrow it down to which set of stops or where in the network data the service area is taking longer to solve? Also, are you using the generalized or detailed methods and what is your trim distance? What is the data source? That is, streetmap or your data?
Another thing to double check is the impedance attribute you are using. What is it, and does it have units of meters? If it has units of, say, miles, and you entered "300" for your break value, then it would be trying to create 300-mile service areas, which could slow it down considerably.