Ruling 738
It is recommended that one perform prayers at the start of their prescribed time; this is something that has been highly advised. The nearer to the start of the prescribed time, the better, unless delaying the prayer is better for some reason; for example, someone waits a little to perform the prayer in congregation, on condition that it does not pass the prime time (waqt al‑faḍīlah).[1]
-Ayatullah Sistani, Practical Laws of Islam, Prayer (Salah)
1
This refers to the early period of the prescribed time for a prayer during which there is more reward for performing it.