I think, there are at least four different ways to deal with split up groups:

1. Switch at a determined (real) time using a timer (as mentioned in the post by MattyMcGrizzle); you could vary here with different time spans, but 10 minutes sounds reasonable to me. I like the idea but it never occurred to me before, so I will try this. A possible problem may be the difference in real time and in-game time, so a fight may need 20 minutes out of game but may represent just 30 seconds in game. My players would certainly complain about this occasionally.

2. Switch at a determined (in game) time (as far as one can tell). This may, though, result in strongly varying time slots for all groups - but it allows you to easily let them split and part later on. This is especially important in scenarios where group A says, they will wait for group B. They will not have the same screen time in this case ;)

3. Switch as fast as possible after break points, e.g. when the discussion in a roleplaying scene gets to a turning point (or ends) respective when a fight turn changes (or ends) etc. Maybe hectic and maybe disruptive, but also may create a dramatic atmosphere.

4. Switch at the best possible point in your story, e.g. when a chapter/discussion ends or a fight ends. May return in long episodes in both sides but may also result in interesting stories with unique dramatic arcs.

I think, there is no optimal way, because there may be a situation where the first way is to be preferred due to the circumstances and in another situation it is the second or the third. Factors may include storytelling, party dynamics or dramaturgical elements. Also you may come to the situation where it is best to give short cuts to group A and longer ones to group B. Being aware of those measures may already help you to find the one that is useful for your actual scenario.

I think, there are at least four different ways to deal with split up groups:

1. Switch at a determined (real) time using a timer (as mentioned in the post by @MattyMcGrizzle); you could vary here with different time spans, but 10 minutes sounds reasonable to me. I like the idea but it never occurred to me before, so I will try this. A possible problem may be the difference in real time and in-game time, so a fight may need 20 minutes out of game but may represent just 30 seconds in game. My players would certainly complain about this occasionally.

2. Switch at a determined (in game) time (as far as one can tell). This may, though, result in strongly varying time slots for all groups - but it allows you to easily let them split and part later on. This is especially important in scenarios where group A says, they will wait for group B. They will not have the same screen time in this case ;)

3. Switch as fast as possible after break points, e.g. when the discussion in a roleplaying scene gets to a turning point (or ends) respective when a fight turn changes (or ends) etc. Maybe hectic and maybe disruptive, but also may create a dramatic atmosphere.

4. Switch at the best possible point in your story, e.g. when a chapter/discussion ends or a fight ends. May return in long episodes in both sides but may also result in interesting stories with unique dramatic arcs.

I think, there is no optimal way, because there may be a situation where the first way is to be preferred due to the circumstances and in another situation it is the second or the third. Factors may include storytelling, party dynamics or dramaturgical elements. Also you may come to the situation where it is best to give short cuts to group A and longer ones to group B. Being aware of those measures may already help you to find the one that is useful for your actual scenario.