Basically, the dealer keeps track of when the blinds double, and prevents new players from joining in mid-tournament. There are a few commands that are enabled only on the tournament channels. Blinds will double at this frequency. Generally in seconds, although you can double by number of hands played if you wish. The small blind will be this size initially.
Large blind is twice the small blind.
New players cannot join after this. Abort the tournament. The current hand can be played out, but after that you're back into the pre-tournament mode. If a person's connection lags or is dropped, you can put them on vacation. This is also useful if you need to take a short break.