When is it too late to unsplit my pension with my spouse?

Not too late but  depend on when pension sharing stops:

According to CRA,

Pension sharing stops in whichever month occurs first:

• the month following the month Service Canada approves a cancellation request submitted by both you and your spouse or common-law partner
• the month you divorce
• the month the spouse or common-law partner who has never paid into the CPP (or QPP) begins contributing
• the month one of you dies

For more information, visit: Pension Sharing

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