Ending Time of Thuhr Prayer
2-10-2018 | IslamWeb
Question:
Assalamualaikum beloved brother, I have an important question regarding the prayer times and possible mistakes in them. Certain prayer times like fajr and asr have more definite moments where they end, but for dhuhr, it might be up to someone’s judgement and discretion when it ends. I know that as long as the person finish one rakaa before the prayer ends, then they catch the full prayer, but for prayers like dhuhr, if someone barely finishes the first rakaa 10-15 minutes before the listed ending for dhuhr, did he complete a valid prayer, or is there a chance that he actually missed dhuhr becaue it was so close. I am worried because I finished the first rakaa of dhuhr 16 minutes before the prayer times said it was over, and I am worried that the time could have already ended for dhuhr. Thank you so much and may Allah reward you and bless you, ameen.
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
Your question is somewhat ambiguous.
There is no doubt that each of the five prayers have a beginning and an ending time, as Allah Says (what means): {Indeed, prayer has been decreed upon the believers a decree of specified times.} [Quran 4:103]
The angel Gabriel 
came to the Prophet and taught him all this, such as the ending time of the Thuhr prayer, which is when the height of the shadow of an object becomes similar to its own height. This is a visible sign that is recognized by the general public, let alone their special (knowledgeable) ones; so whoever completes one Rak’ah before this time, then he has indeed prayed on time.
If the situation is as you mentioned, that you started praying about 16 minutes before the end of the time of the prayer, then this time is enough for a Muslim to pray the whole prayer on time, let alone praying only one Rak'ah on time, so be reassured and do not open the door of whispers.
Nonetheless, if there is anything that we did not understand in your question, then please clarify it to us.
For more benefit, please refer to Fataawa 92246 and 92052.
Allah knows best.