Heart Rate variation at different times of the day

I would be keen to hear peoples thoughts on how heart rate changes from a morning workout to lunchtime or afternoon workout.

This morning I did Carillon and my heart rate was where it normally is for morning workouts.

Yesterday I did bald knob an easy workout and my heart rate was the same but the ride was recovery and power output well less.

I have noted that any session I do later in the day seems to be the same, with a higher heart rate. Is this a normal difference with people?

Typically my RHR is lowest between breakfast and lunch. On workouts, in the morning, my HR is usually higher at the begging and during the low efforts but will normalize 30-40 minutes into it. Likely because I just pounded a coffee breakfast.