Not a founder, but I did this as an exercise about two months ago. The answer? 15 minutes.The founders should try to re-join as new users and see how long it takes them to build up a meaningful feed.
So. This account is like 70 days old or something and exists solely so for testing something we created solely for the purposes of aiding new users. However, if you check my feed you will see that it has content and articles and stuff in it, all of which it gained in the past three minutes. The first thing I did was click on "badges" in the upper right. I then saw a post by insomniasexx that appealed to me, so I clicked her name. I then had the option to follow her. I looked at some of the other stuff she posted, and clicked on one of the tags she used. This led me to an interesting article by @butterflyeffect@, so I also clicked on his name and followed him. I then looked over the stuff he posts and clicked on one of his tags, which I am now following. As a result, in the space of five minutes I'm following two users and three tags: #space, #goodlongread and #relationships. Note that these are self-evident tags; they present no surprises, unlike #writebetterdammit. Note that I needed to only click on "badges" once in order to get a heapin' helpin' of high-quality content, and from there it was like pearl-diving Wikipedia. Good luck and god speed.