Answered by Sidi Fadi Qutub Zada
One of the conditions of being mazoor [having a chronic excuse] is that the problem must exist for an entire prayer time. so if one wakes up for fajr with olny 20 minutes to go and cant hold his wudu is for some reason is that the entire prayer time for him or is the entire prayer time from the start of fajr to the end of fajr
In the Name of Allah, Most Compassionate, Most Merciful,
One’s chronic excuse (`udhr) is determined by the second prayer time.
Imam Ibn Abidin says: “if a chronic excuse occurs after a fard prayer time had entered, one waits until the end of the time. If the excuse does not discontinue, one performs wudu and prays. Then, if it discontinues within the second time, one repeats that prayer [f: that one prayed in the first time]. If it remains through the second time, one does not repeat.
For example, Khalid gets a nosebleed twenty minutes into dhur. He tries to stop the bleeding, but he can’t, so he waits until just before the end of dhur time to see if the bleeding will stop. It continues to bleed, so he makes wudu and prays. When Asr comes in, his nose is still bleeding. It bleeds throughout the time, without giving him a chance to perform a minimal wudu and pray without blood dripping. Khalid is now legally considered to be someone with a chronic excuse, and he does not have to repeat the dhur and asr prayers. If Khalid had time during asr to perform a minimal wudu and pray without his nose bleeding, then he will not be considered as someone with a chronic excuse, and he will have to repeat his dhur prayer.
And Allah knows best
Fadi Qutub