Question

you know,this is the first saturday i've had off in months.

Answer 1

这句话强调这周六假期是很多个月以来"难得的休息"=
I
have
had
off
in
months
only
on
this
first
Saturday.
You
know
则只是口头禅。

Answer 2

回答如下
you
know插入语,this主语
is系动词
the
first
定语saturday
表语（省略了that,
i've
had
off
in
months.)定语从句
你分析的定语从句是对的
这里that在定从里做have
had的宾语，而后面别忘了还有一个off，表达的意思是i
have
had
the
first
Saturday
off
in
months，表达的的确就是"几个月以来我休的第一个周六假期”。