ANSWER:

The end time for praying maghrib is when the redness in the horizon is gone, which would approximately be 70 minutes from sunset, depending on the country. If you pray it within the prescribed time, your prayer is valid.

I know that Maghrib lasts until Ishat time starts. In the UK currently Maghrib is about 6pm and Ishat is about 7:20 according to mosque timetables. I’ve heard that Maghrib should be prayed very soon after it starts, someone even said 20 minutes. But if something makes it difficult for me to pray Maghrib straight away and I pray at 7 or 7:10 would that be ok?