The longest flight (in a single day) happened while advancing from Mazatlan (MMMZ) to Oaxaca (MMOX) with a refueling stop in Morelia (MMMM). The first leg of the flight was through good visibility air and broken clouds. Surfing those clouds was amazing and very relaxing. However, the situation after MMMM changed dramatically, with low ceiling, low visibility, 10,500 feet mountains, rain and thunders that we could hear in the intercom. Still, we were in mood to enjoy some food that we purchased at the airport eatery. The whole flight was supposed to cover like 650 nautical miles in 6.5 hrs but we ended up doing it in 7.5 hrs due to going around the thunderstorm. As a result, we landed in Oaxaca under rain and during night time, something against Mexican law if flying VFR. I apologized and managed to get away without a fine.