Want to make my sentence clear and neat

[kwfine]

Say, on the 25th of January, I was eating a cake from 8:00am to 7:00pm.
I was eating chocolate at 8:00 p.m.
Now I want to use the word "since" to build a sentence to describe what I was doing on Jan 25.

Is this correct:

I had been eating a cake since 8:00am before I started to eat chocolate at 8:00 p.m.

Thank you.

[Alan]

Yes.