Assalamualaikum w.b.t. Is it an obligation for the solemnization to be uttered in one breath?
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
Nikah (solemnization) according to the 4th Edition of Kamus Dewan means an akad (agreement) that contains the utterances of ijab and qabul that permits a man and woman to have intercourse. 
The word nikah is mentioned in the statement of Allah SWT:
فَانْكِحُوا مَا طَابَ لَكُمْ مِنَ النِّسَاءِ
“Then marry those that please you of [other] women,” 
Islam encourages its ummah to get married for it is included as an action that is a part of the sunnah of the Prophet PBUH. Furthermore, marriage has many other advantages and benefits whether for an individual or even society. This is stated in a hadith narrated from Abu Ayyub RA, the Prophet PBUH said:
أَرْبَعٌ مِنْ سُنَنِ الْمُرْسَلِينَ: الْحَيَاءُ، وَالتَّعَطُّرُ، وَالسِّوَاكُ، وَالنِّكَاحُ
“Four matters that are among the sunnah of the messengers are shame, wearing perfumes, brushing teeth and marriage,” 
In fulfilling the commandments of a marriage, a person cannot run from fulfilling the commandments of syarak which is for the marriage to be complete and perfect. Thus, it is obligatory for a person who wants to get married to fulfil the requisites and conditions of marriage in order for it to be valid. Dr Muhammad Zuhaili stated that a complete solemnization will only be fulfilled when all of its requisites and conditions are fulfilled. 
The author of al-Fiqh al-Manhaji  stated that there are five requisites for the solemnization of a marriage and they are:
- Two witnesses
Dr Muhammad Zuhaili further detailed the requisites of solemnization into six which are Sighah (ijab and qabul), al-A’qidan (groom and wali), bride and two witnesses. 
Sighah means an utterance or action conveyed by a person that is doing the akad (agreement) to show his willingness. Jurists are of the opinion that the matters contained in the sighah should include ijab (the utterance of offering) and qabul (accepting utterance). 
Dr Muhammad al-Zuhaili in al-Mu’tamad stated that the solemnization of marriage isn’t valid except with a sighah of ijab and qabul. Originally, sighah only involves two parties which are the groom and the wali:
- Ijab means the offering utterance from the wali of the bride which states “I marry you” or “I offer marriage to you” and others.
- Qabul means the utterance of acceptance from the groom by stating “I accept” or “I agree to accept this marriage” or “I agree to marry”
According to the above question, it isn’t conditioned for it to be in one breath. However, the real condition is for it to be done consecutively following madhhab Syafie.
The author of al-Fiqh al-Manhaji said: Among the conditions of the utterance of solemnization with ijab and qabul by the groom should be done consecutively. If the wali said: “I’m marrying you to my daughter,” and after a long period the groom answered: “I accept this marriage”, the marriage isn’t valid. The reason is the long separation between the ijab and qabul. During this long period, there is the possibility the wali to retract his ijab. As for a slight pause between ijab and qabul, such as to take a breath or sneeze, it doesn’t affect the solemnization. 
However, according to madhhab Hanafi and Hanbali: It is fine even if there is a long separation between the ijab and qabul if it is still in the same ceremony but one is distracted or busied with another matter.
To close, we’d like to suggest the imam and person holding the solemnization to ease the process of the solemnization utterance and not make it difficult when it has fulfilled all of its conditions. This after considering the nerve-wracking situation the groom is in and others.
May Allah SWT grant us all understanding in His shariah and ease all our affairs. Amin. We end with the supplication:
رَبَّنَا هَبْ لَنَا مِنْ أَزْوَاجِنَا وَذُرِّيَّاتِنَا قُرَّةَ أَعْيُنٍ وَاجْعَلْنَا لِلْمُتَّقِينَ إِمَامًا
“Our Lord, grant us from among our wives and offspring comfort to our eyes and make us an example for the righteous.”
 Surah Al-Nisa’: 3
 Narrated by al-Tirmizi (1080) and Ahmad (23628)
 See al-Mu’tamad fi al-Fiqh a-Syafi’e, 4/53
 See al-Fiqh al-Manhaji, 4/55
 See al-Mu’tamad, 4/53
 See al-Mausu’ah al-Fiqhiyyah al-Kuwaitiyyah, 30/200
 See al-Mu’tamad, 4/53
 See al-Fiqh al-Manhaji, 1/551-552