It is best to schedule the change to happen on the same day as your billing cycle date.
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TRYSPI, that's a great question to ask. Depending on the kind of plan change you want to make, determines when the best time is to make it. In general, Ann154 is correct that it's always a good idea to set plan changes to begin at the start of a new billing cycle. If you could share more about the type of plan change you want to make, we could give you a more specific answer.
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