Praise be to Allah.
It is not permissible to delay prayers beyond the time when they are due, because Allaah says (interpretation of the meaning):
“Verily, As‑Salaah (the prayer) is enjoined on the believers at fixed hours” [al-Nisa’ 4:103]
“Then, there has succeeded them a posterity who have given up As‑Salaah (the prayers) [i.e. made their Salaah (prayers) to be lost, either by not offering them or by not offering them perfectly or by not offering them in their proper fixed times] and have followed lusts. So they will be thrown in Hell” [Maryam 19:59]
Islam has told us the times of the prayers, as described in the hadeeth which was narrated by Muslim (217) from ‘Abd-Allaah ibn ‘Amr (may Allaah be pleased with him) from the Prophet who said: “The time of Zuhr is so long as the time for ‘Asr has not begun, and the time for ‘Asr is so long as the sun has not begun to turn yellow, and the time for Maghrib is so long as the afterglow has not faded, and the time for ‘Isha’ is until midnight, and the time for Fajr is so long as the sun has not yet risen.”
In the answer to question no. 9940 we have explained the times of the five daily prayers in detail.
It is sufficient here to mention the end of the time for each prayer.
The end of the time for Zuhr is when the time for ‘Asr begins.
The end of the time for ‘Asr is when the sun starts to turn yellow; the time is extended in cases of necessity, such as when a person is sick, etc., to when the sun sets.
The end of the time for Maghrib is when the red afterglow disappears from the sky, which is the beginning of the time for ‘Isha’.
The end of the time for ‘Isha’ is midnight (halfway through the night), and it does not last until the time when dawn begins.
The end of the time for Fajr is when the sun rises.
It is permissible to offer the prayer at any point within the time for that prayer, whether at the beginning, in the middle or at the end. It is not permissible to delay any of these prayers until after its time is over without a valid excuse such as sleeping or forgetting.
Based on that, praying Zuhr half an hour or a quarter of an hour before ‘Asr is valid, and there is no sin on you in that.
With regard to ‘Asr, you must pray it before the sun turns yellow, and the timing of that varies from one season to another. It seems that quarter of an hour before Maghrib the sun will have turned yellow, so the time for ‘Asr will be over.
It is not permissible for you to delay ‘Isha’ until half an hour before Fajr, because the time for ‘Isha’ is up to midnight, as it says in the hadeeth. If you want to work out when midnight is, then calculate the time from sunset until dawn, and half way between the two is the end of the time for ‘Isha’ (this is midnight). If the sun sets at five o’clock and the adhan for Fajr is given at five o’clock, then midnight (or half way through the night) is eleven o’clock at night.
It is better to hasten to perform the prayers when the time for them begins, because of the hadeeth narrated by al-Bukhaari (496) and Muslim (122) from ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased with him) who said: I asked the Messenger of Allaah (peace and blessings of Allaah be upon him), “Which deed is most beloved to Allaah?” He said: “Prayer offered on time.” He said, “Then what?” He said, “Honouring one’s parents.” He said: “Then what?” He said, “Jihad for the sake of Allaah.”
And Allaah knows best.