Harden them off gradually to the outdoors then go ahead and plant.

Congratulations on your purchase. I have been looking for that one locally but have not had much luck. If you go to weather.com's 10-Day Weather Forecast Page, you can keep an eye on the lows for the coming week. Input your zip code or city/state on the page. I normally put them under a tree -in full but bright shade- and then on morning sun only. If they came out from under winter protection and the stems are whitish, I keep them in shade longer (in full but bright shade) until the stems turn green. If yours had been paniculatas, you could then move them to full sun; but the other hydrangeas normally like some afternoon/evening shade. Annabelle's cousins -like Wee White- must have only morning sun in the summer in the South but, it may be able to handle more summer sunlight in northern locations. Feel free to transplant it if it displays too much heat stress during the summer months, as temperatures zoom past 85F on a regular basis.

I'd say it depends on what stage of growth they are in. Dormant, green and growing or somewhere in between? And typically what is published is the average last frost date so you should still check the forecast if it's in a frost or freeze sensitive stage of growth.

Pennlake, they are in 3gal pots and leafed out with new growth coming. No buds yet, but it’s way too early for that anyway. Our ”last” threatened frost date is this Wednesday, and after that lows will warm up to the 40’s so I may plant this weekend.

My other Wee whites (3 from last year) are leafed out and look just like the new ones, but smaller (they were bought at 1gal plants last year). Those I bought in Aug and (yes, i know i shouldn’t have) i went a head and planted them...but I babyed them like crazy and they did well...except for 1 who is super small compared to the other 2.

Can’t wait to plant these!