Hello M, Kenn: First of, there is only one flight by Druk Air for this October, which is planned to depart at around 1PM. Another new airline – Bhutan Airline is planning to commence its flight as well starting May 2014 but there is no way to know for sure.
To your second question, if your flight arrives in the morning 6:15Am in Kathmandu and if you trying to connect same day around 8:45AM it is not recommended, if there is a flight.
There may not be enough time to retrieve your luggage, go through immigration etc and check in again. Besides, as you yourself pointed, due to weather flights are not always in time.
Delays due to low fog in Kathmandu can be more frequent after November, and through-out the winter months (up till mid Feb). October and November, March and April are generally good. In the summer there are sometimes delays due to excessive rains or wind.
But we are talking of weather, which can change any time, especially in the Himalayas. It all boils down to how much time you have. If you are extremely short on time, then you have to take chance with weather. Otherwise plan on extra time, extra day and contingent time . These will save lots of hurdles.