How do I phase out clear retainers to night wear only?

I've just finished my clear aligner treatment, and the results are great. I'm now wearing the clear Vivera retainers, and my dentist told me how to phase them out to night wear only ... but I have completely forgotten what he said, and its tough to get in to see him as he's so busy and much sought after. Can anyone remind me how to phase out my retainer to night wear only? A sort of reduction schedule etc. Thank you in advance.

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