Almost all nurseries, garden centers, and big box stores will have dolomitic (garden lime) now or soon. The purpose of the lime in the 5:1:1 mix is twofold. It raises pH to what is a more favorable level for most plants, and serves as a source of both Ca and Mg. You CAN make the 5:1:1 mix w/o it for plants that prefer a more acidic medium, but it's not necessary. The best way to control pH is via the pH of your irrigation/fertigation water. If you DON'T use lime, you need to be sure you are supplying both Ca and Mg in your fertilizer (most soluble fertilizers lack both Ca & Mg) or by including CaSO4 (gypsum) in your soil and including some MgSO4 (Epsom salts) in your fertilizer regimen. Gypsum and Epsom salts contribute Ca ans Mg (respectively) w/o any significant impact on the p[H of the soil or soil solution.
I remove ALL of the old soil from everything I pot or repot in the gritty mix. I sometimes do it over 2 repotting sessions in consecutive years, but I do try to be sure I don't leave any of the old soil on the roots.
No need to let the gritty mix rest under any circumstances. The 5:1:1 mix would be better left to rest for a week (if it's moist) so the Ca can get through the reactive phase to where there is a residual fraction that is more readily available for uptake. That said, I very often plant in 5:1:1 I made the same day. I do try to use soil that I made a week earlier for anything prone to BER, though.
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