Why 24 October? It’s the last Thursday before exit day, so the last likely polling day that could lead to a pre 31 October change of Government.
The Crown’s proclamation for setting polling day therefore can’t be later than Wednesday 18 September.
14 day period begins with day after day on which a VONC is passed. So the vote must take place no later than rise of Commons on 3 September.
This is, if you believe some press reports, the day after it is expected Theresa May may step down as PM.
(a) the possibility that MPs may wish a period of “wash-up” to get some outstanding legislation through. That would add an additional week of pressure to the above timetable.
(c) possibility of Governemnt seeking a GE quicker (a 2/3 majority as with the 2017 one).
(e) possibility that a Government can gain/regain the confidence of the House on or before Tuesday 17 September.