I think I tend to have faster roots-to-side-of-cup times because I expect such high rooting activity inside the bag (1/2" or more, usually) before placing in the cups.
I received two Chico Strawberry cuttings from a fig friend in the last week or so, and they arrived with 3"-4" of roots stuck to the paper towels! Put them in cups after soaking for a minute to free the paper towel without ripping all the roots off (lost some in the process), and saw roots against the cup in 4 days.
Likewise, I got some other cuttings from another fig friend over a month ago with a Vern's BT, and it had great roots in the baggie in 5-6 days. I transferred that cutting to a cup ~3 weeks ago, and still no roots appearing, but the leafing has continued, and I expect maybe to see some roots against the sides of the cup in 1-2 more weeks, if lucky.
It varies a lot based on the variety of fig, the cutting location (near trunk or peripheral), the cutting size and thickness, the potting matieral you choose, how much water, temperature, humidity.
I have one variety that half a dozen members can vouch for at this point - "Unknown Voiture 217" - it can take 2-3 months to set a root in the baggie, but when it finally roots, the thing freaking explodes. You will have a pile of spaghetti on your hands before you see a single bud break. Then you have varieties like a Latarrula I picked up from another fig lover which set roots really fast, but still hasn't broken bud yet, the complete opposite of my voiture Unknown.
I have had cases where cuttings will root in the bag, then you put them in the cup, and they do nothing but sit there for months, growing leaves but showing no roots and others that just "fizzle" out (shrivel/dessicate, usually the smaller/skinny cuttings).
There are a lot of folks around here with much more experience at fig rooting than I have. These are just some things I can share from first-hand experience. My logic is the same as anything else I've ever rooted, if you're showing a couple of strong roots in your prepping method of choice (in the bag for this case), then you know for a fact that rooting has begun and you can forego guessing about whether the cutting is rooting, which is something you always need to guess about if you direct-root to the cup (skipping the baggie).