[Talf]

where did,
rules change on the first day,
come from?
...

I though that the Senate was a ‘continuing body’
so rules would continue from the
last session, ..unless changed..

[Kegger]

I though that the Senate was a ‘continuing body’ so rules would continue from the last session, ..unless changed..

I believe you are right. Further, I think it takes 2/3rds of the entire senate for a rule change.

[Blood of Tyrants]

Continuing from when? Until when? Who decides?

The Constitution only says that the Senate has the power to set its own rules. The Senate can st them and change them at anytime.