- Firts of all the term sobh/subh (or as-Sobh/as-Subh) الصبح appears in a whole lot of ahadith referring to the fard (obligatory) prayer which is performed after the real fajr الفجر and this term is used by the maliki scholars to refer to this prayer while many others refer to it by the term the fard of fajr.
See for example in Sunan an-Nasa-i:
"The Messenger of Allah (ﷺ) prayed Subh as soon as he was certain the dawn had appeared."
- "As-Sobh" in Arabic also literally means the morning.
For example it is quoted in the hadith explaining how to perform the night prayers (however it was translated in that case otherwise on sunnah.com, except for the version of Riad as-Saliheen):
man stood up and said. Messenger of Allah, how is the night prayer? The Messenger of Allah (ﷺ) said: The night prayer consists of pair, but if you apprehend the rise of dawn, make it odd number by observing one rak'ah. (Sahih Muslim, Sahih al-Bukhari, Jam' at-Tirmdihi and Sunan an-Nasa-i and also in Riad as-Saliheen)
Finally if a person misses to pray the witr prayer before the fajr (dawn) he can pray it before praying fajr and sobh this view is held by the maliki school of fiqh which considers it a time of necessity for witr and also is considred as poermissible by the hanbali school of fiqh, while the majority considers this time as invalid for praying witr. Among the main evidences for the maliki and hanbali school you'll find:
Observe Witr prayer before it is morning. Abu Sa'id reported that they (the Prophet's Companions) asked the Messenger of Allah (ﷺ) about Witr (prayer). (In reply to their inquiry) he said: Observe Witr prayer before it is morning. (Sahih Muslim and in other hadith compilations)
“The Messenger of Allah (ﷺ) said: ‘Whoever sleeps and misses Witr, or forgets it, let him pray it when morning comes, or when he remembers.’” (Sunan ibn Majah)
"When Fajr begins, then every Salat of the night and Al-Witr have gone, so perform Al-Witr before Fajr begins." (Jami' at-Tirmidhi)
أن أبا الدرداء كان يخطب الناس أن لا وتر لمن أدرك الصبح فانطلق رجال من المؤمنين إلى عائشة فأخبروها فقالت كان رسول الله صلى الله عليه وسلم يصبح فيوتر
Here and in the following when I quote Arabic text and an English transaltion these are own translations take them carefully
Abu ad-Darda' was holding a seremon and told the people that there's no witr prayer if morning (dawn) appears, some men hurried to the mother of beleivers 'Aishah and informed her and she said: The messenger of Allah Allah's prayers and blessing be upon him used to pray witr if morning (dawn) appeared. (Musnad Ahmad and in at-Tabarni's al-Mo'jam al-Awsat -sources in Arabic-)
Yahya related to me from Malik that Yahya ibn Said said, ''Ubada ibn as-Samit used to lead the people in prayer. One day he came out for subh and the muadhdhin began to give the iqama for the subh prayer Ubada silenced him, prayed witr and then led them in subh." (Al-Muwatta' where you may find further evidences)
According to this praying witr after dawn certainly is not the preffered time to pray witr in the maliki madhhab as the time of necessity is not considered as a time one is recommended to pray at.
The preferred time to pray witr
Finally there's a consensus among scholar on the time of witr (the time in which it is recommended to pray the prayer of witr) even if they may have difference of opinion on the preffered amount of raka'as of witr and whether this time apply also for the case that one may prayr Maghrib and 'Isha as joint prayers in jam'a taqdeem (before 'isha' time). The maliki school of fiqh in the later case holds the opinion that the time of witr is independent and stays the same for any case.
Ibn al-Mundhir ابن المنذر in his book called al-Ijma' الاجماع (The consensus) which includes all what sunni scholars have consensus about says:
أجمعوا على أن ما بين صلاة العشاء إلى طلوع الفجر وقت للوتر (Source: See #76 in this google book)
They have consensus that between the (time of) 'Isha' and break of the dawn is the time of Fajr
This is due to the second hadith I've quoted in my answer and the narrations saying:
Allah the Exalted has given you an extra prayer which is better for you then the red camels (i.e. high breed camels). This is the witr which Allah has appointed for you between the night prayer and the daybreak. (Sunan abi Dawod, Jami' at-Tirmidhi and with a different wording in Sunan ibn Majah)
So far we made clear when witr should be done. Note that the malikis say that the time of 'Isha' referred to is the time of the real 'Isha' (as mentioned in the hadith of prayer timings see for example in al-Muwatta' and Sahih Muslim)not the time one may pray 'Isha' at due to a legal permission such as travel.
As for the preferred time we have in the sunnah:
"Make witr as your last prayer at night." (Sahih al-Bukhari, Sahih Muslim)
so it is most recommended to pray it in the last part of the night (many scholars say: the last third of it) or before going to sleep. Note that the ahadith on witr and the fact that it is recommended to pray some sets of night prayere before it even support this.