Is it permissible to combine the Maghrib and Isha prayers due to heavy snowfall if dinner is eaten and one remains in the mosque for approximately an hour after the Maghrib prayer?

If the conditions for the validity of combining prayers by advancing them are met, namely: the intention to combine at the time of declaring ihram for the first prayer, performing the two prayers consecutively, and the presence of a permissible excuse for combining, such as rain, at the beginning of the first prayer, upon concluding it, and at the beginning of the second prayer, then your combination is valid and nothing is incumbent upon you, even if you remain in the mosque until the time for the 'Isha' prayer begins. Hanbali jurists have explicitly stated the permissibility of combining for someone residing in the mosque if an excuse exists. However, it is preferable, if you know that you will remain in the mosque until the 'Isha' prayer time, not to combine, as the hardship is absent. Thus, separating the prayers is better, with the exception of combining prayers at 'Arafat and Muzdalifah.