You'd just owe on that $5.

All that's happening with a "backdoor Roth IRA" is that you're converting from one tax status to another, and you owe taxes on any untaxed money. If you took a deduction on your IRA contribution, that money would be untaxed going in, and thus taxed when you convert. Since you're doing a "backdoor" IRA, I assume you're not taking the deduction, so the only taxes due would be on any gains.

It doesn't matter if you waited a year or more, all that matters is what taxable bucket the dollars are in when the transfer is made.