That sounds like a wonderful start!
When something goes well, I like to repeat it a couple times before making any big changes. So you could do a couple more 30 min sessions, and then if those go well bump up to an hour, then may 2 hours, etc. If you are busy on certain days and can’t do a long session, that’s OK, a short session is better than no session, and some people will also do multiple short sessions in a day if it works better for their schedule.
When you get to the point where they are doing well in 2-hour-ish sessions, you could try some longer ones on the weekend, like 4-6 hours. If those go well, you could try for an overnight on the weekend (supervised of course!). My first pair I just did a few supervised overnights in a row, rather than 24/7 marathoning, because it just worked better with my schedule. Trouble usually happens at night, so those overnight sessions tend to give you a good picture of where they are at.
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.