Cash account (not margin account) normally needs 3-4 days for clearing. You can ask your broker for exact days for showing the available funds for new buys.
Is your CDN RRSP account a margin account?
In US 401k account, the company-specified brokers mostly have the limitation for re-buying the funds (after one month?). But we can trade the funds anytime when there is available cash in any IRA broker account.
Not sure how CDN RRSP account works (http://www.investopedia.com/university/rrsp/rrsp1.asp). You can contact your broker of your CDN RRSP account for correct answer.