There are numerous well-known obligations to prayer, as established throughout the hadith literature, including rulings on the form of prayer, the daily number of prayers, praying in congregation, and where and when such prayers are to be done.
However, given that many of the hadiths in question, despite their authenticity, are not clearly dated, it is hard to know which of these obligations were in place before the first masjid was built (i.e. before the Hijra), and which of these obligations were only established afterwards.
For example, the well-known hadith of the man who prayed badly is often referenced to describe what is mandatory in regards to the form of the prayer. The timing of this hadith, however, is likely after the Hijrah as it is narrated as taking place in the masjid itself ("Allah's Messenger (sallallahu 'alaihi wa sallam) entered the mosque and a person followed him...") While the man himself clearly did not know the proper form, it is not clear whether this form was commonly known or mandated previously.
Given that the revelation to the prophet began about a dozen years earlier, even without the firm political base of Medina with which to establish (and enforce) legislation, it seems there likely would've been some regulation, at least for one of the most fundamental aspects of the religion (one of the "pillars", as it were).
Is there any information regarding which (if any) of the prayer obligations were in place before Hijra?