There are two times for Asr; preferred time and this is from athan of Asr until the sun becomes yellow and one can look at it. The second time is a time of necessity and this is not recommended and it is from the time the sun becomes yellow till it sets!

I want to know what is the maximum time before Maghreb upto which one can offer Asr Salaah. For example, if Maghreb starts at 6 pm and I’m not in a position to offer Asr Salaah in school, then before what time can I offer it?