If you like longer sessions (I do.), then it's pretty important.

Some hobbyist are the stereotypical wham, bam, thank you maam type and that's just fine too.

I like to click with the gal and spend some time socially.

How important is it to find mutual interests or good chemistry in downtime?

I will typically set up two hour initial dates as finding a chemistry is important to me with a lady.  As I have been moving through this "hobby", I am finding that only a few of the ladies intrigue me enough to see for longer dates (four hours and more).  Where I have these longer dates the chemistry is right and the afternoons fly by.  Having the chemistry and communicative skills is paramount in making this date work.  A good amount of time on a four hour date (at least with me) is spent out and about, and while a number of the ladies I have seen are eager to embark on that with me, I tend to do so only with a lady that I have found that chemistry with after an initial date.  As the relationship grows I am finding that even longer dates (eight plus hours) are more stimulating, with the public time being a significant portion of this date.  Finding that lady who is able to keep your interest there for extended periods of time is my goal with each lady I see.  But ultimately only a few ladies thus far have been able to accomplish that with me..but I keep an open mind with any new lady I do see.

If you plan to be there more than like a half hour...i'd say something clicking is extremely important.