Converting a contribution to a Roth IRA >60 days after contributing?

The length of time money is in Traditional IRA before you convert it to Roth IRA has no relevance to the taxes. What matters for taxes is the amount that is converted and the year it was converted in, and also how much after-tax contributions there were in the Traditional IRA compared to the total value in Traditional IRA.

If your Traditional IRA funds are invested, and they grow over time, then if you wait a long time, it is more likely to have grown, and thus there will likely be more taxable income when you convert it; but that just has to do with the amount converted, not the length of time since contribution. And if you wait until a future year to convert, then the taxable income due to the conversion will be taxed in a different year; but again, this just has to do with the circumstances of the conversion and not the length of time since contribution.