How did you decide there were 105 possibilities?My answer is:
There are 420 possible morning arrivals and out of those 420 possibilities, there are 105 possibilities that they arrive within 5 minutes between each other.
If Afra arrives at 7:00 then Wiro has a 6 possibilities (7:00, 7:01, 7:02, 7:03, 7:04, 7:05) of arriving within Afra's waiting time.
If Afra arrives at 7:01 then Wiro has a 7 possibilities (7:00, 7:01, 7:02, 7:03, 7:04, 7:05, 7:06) of arriving within Afra's waiting time.
It seems to me that the closer Afra arrives to the 7:05-7:15 range, the better the chances get.
You could consider making a table of the 21 cases (don't panic, the 11 cases in the middle seem to have the same outcome so it's not a ton of work).
I haven't done the work to calculate this but I believe they have better than 25% odds for riding together.