Yesterday, the total time wasted at all the stations was 321 minutes. If we assume a 5-minute stop at each station on average, it would only take 75 minutes. So, the actual extra time added to the timetable is 321 - 75 = 246 minutes. This includes 11 minutes of late departure and 8 minutes of arrival before schedule. That means we have an extra 4 hours and 25 minutes, which is equal to 265 minutes. Let's consider a buffer of 2 hours. Even after that, we still have a chance to speed up by 2 hours and 25 minutes.