Those plants will be smaller and may or may not be in bloom, but they should be in bud. When you buy plants, look for healthy, green leaves with no discoloration above or underneath. Select plants with fairly compact growth and good branching. If you can't plant the zinnias the day you bring them home, water them well and set them under a tree or patio cover where they'll be protected from the drying effect of direct sun. Planting Zinnias Selecting a site.
Zinnias grow best in full sun, which means six or more hours of direct sun daily.
In desert locales and Zones 9 to 11, choose a site that gets some shade at midday and in the late afternoon. Preparing the soil. Transplanting into the garden. The best time to transplant any plant is on a cloudy day or in late afternoon so that the plants have a chance to get settled in before they have to contend with the drying effects of the sun. Set zinnias in the ground at the same depth they were growing in the pots.