The best time to perform it is on Friday before noon. This prayer can be counted as the Nafila of the night or the Nafila of the day.
Additional Info:
Salaat of -Ja’far-e-Tayyar (brother of Imam Ali (as) is among the prayers that are greatly emphasized and it is famous among all sects. It was a gift of love bestowed by the Holy Prophet ( s.a.w.s.) to his cousin upon his return from the journey.
Imam Sadiq ( a.s.) has said: 'On the day of the conquest of Khyber when Ja’far returned from Abyssinia the Holy Prophet ( s.a.w.s.) asked: 'Don’t you want a reward? Don’t you want a gift?' Hazrat Ja’far replied: 'Why not, O Messenger of Allah?' The Messenger of Allah ( s.a.w.s.) said: 'I am giving you something that if you perform it everyday it would better than all those things that are present in the world. And if you perform it once in two days the Almighty will forgive the sins of both these days and if you perform it every Friday or every month or every year the Almighty will forgive all the sins committed in between.' '
Imam Ja`far al-Sadiq (as) : 'If you have a significant request and you want it to be granted, you may offer this prayer, say this supplication, and implore Almighty Allah to respond to you. If you do, it will be granted, Allah willing.'