Do these sound natural?
1) I will let you know when it's nearer the date.
2) I will let you know when the date is nearer.
They're grammatically OK, but I can't imagine myself saying them....when the date draws nearer/closer.
All the alternatives given in the responses are grammatically correct but they don't change the fact that, in BrE, it's generally "I'll let you know nearer the time". That works whether the thing under discussion is a date or a time.
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