I believe that starter engagement time limitations for most engines are not published primarily to limit the time the pilot uses the starter for a normal engine start, they are published to limit the time that a maintenance technician uses the starter for dry motoring, engine washes, and other non-flight related activity.
Common sense suggests that when the aircraft manufacturer publishes a starter engagement time limit, they will have ensured that the limitation allows sufficient time for a normal engine start. Thus, if pilots are running up against the starter time limits, this suggests that the there is a problem elsewhere that needs to be investigated - in other words, why is it taking longer than normal to start the engine?
Just food for thought.