Hi Schwartzie,
I find playpen time very useful for my ham as she's cage aggressive, so I really only get to interact with her directly when I take her out into her playpen. I usually do this every other day as she is quite stressed in her nature so I give her a day to chill, but I also take note if she seems especially stressed that day and will leave it for an extra day if need be. I use a diy playpen I found online which is a cube storage unit with the panels instead attached in a row with zipties. It works well apart from the fact she can push it up if she gets a hold with her teeth so I have to watch her carefully!
I do also have cats, but I make sure my cats have absolutely no access to the room she's in pretty much 100% of the time as I'm certain if they even knew she existed they would stake out the room constantly, so they've never seen her! But I am sure my ham can smell them on my clothing and carpet and she doesn't seem bothered (although she is a generally stressed hamster so she spends most of her time running at 100mph and trying to escape the playpen anyway!!), but maybe try putting a blanket or sheet on the floor in case
