Sforno on Genesis 1:5/ספורנו על בראשית א׳:ה׳

1ויקרא אלוקים לאור יום; even though at that stage of creation “time” was not yet an operative term as we know it nowadays, i.e. the terms “day” and “night” were not yet used by anyone, G’d named these phenomena as such already at that time.

2ויהי ערב ויהי בקר, although G’d had made a separation between the light and the darkness, assigning to each different time frames in which to be active, independent of the planet earth revolving on its axis, He arranged for a transition from one phenomenon to the other to take place gradually, step by step. This occurred by means of inserting a period known as evening preceding total night, and a period of dawn preceding bright sunlight, daylight.