DavecUK usually within a year, if there is an actual business there, you would be looking for a bigger roaster
Definitely that is how a lot of roasters do it, but some can stay on smaller roasters for a while.
Roasters like Rose, Space and Ride and Grind have been on 1kg toasters for a couple of years now.
Source coffee roasters actually downgraded from a 5kg roaster to a 2.5kg roaster because they focus on high end lots so the smaller capacity is better for them so they can roast more variety
But yeah a lot of roasters move quickly to something like a used probat 5kg up to 15kg or a diedrich ir-12 which are very common, or a smaller giesen w6a and stay there for a long time. Cult and Unorthodox both run great businesses from a 6kg roaster.