The Religion is Easy
Abu Hurayrah (radi Allahu anhu) reported that the Prophet (sal Allahu alaihi wa sallam) said, “The religion (of Islam) is easy, and whoever makes the religion a rigor, it will overpower him. So, follow a middle course (in worship); if you can’t do this, do something near to it and give glad tidings and seek help (of Allah) at morning and at dusk and some part of night.”
Besides moderation in worship, this Hadith enjoins that such times should be fixed for worship when one is fresh so that one feels pleasure in performing it. But this principle is for optional and voluntary prayers only. Obligatory Salat are to be performed at the prescribed times only.
And Allah Knows Best!