I would cut the petiole string that connects the leaf to the stem. Hydrangea macrophyllas will probably have invisible flower buds inside the ends of the stems now so, cutting stems needs to be avoided or you may loose Spring 2021 flowers. You may get new foliage now, later in the Fall or in Spring 2021... whenever the plant decides to do it. On the one hand, winter is approaching, there is now less sunlight and there are slightly lower temps which may promote the start of dormancy but, on the other hand, the plant will probably not go dormant just yet (probably around December-January in NW Florida, no?). My hydrangeas normally go dormant from mid to late November to the first half of December. Note: green leaves (and partially green leaves) produce food for the roots to use/store during winter so avoid removing "too many" partially green leaves. It may be best to remove the completely browned out leaves; those that are green/partly green now but that brown out in the next 30 days; and those leaves that are desiccated and feel papery to the touch.

91 degrees is usually not a problem for hydrangeas but like you said, these were "new" plants. As long as the plants have mulch and the soil is kept as evenly moist as possible, the leaves can handle temps above 110F here without dying immediately (but the leaves will sulk and wilt). They do require dappled sun or morning sun only (sun usually thru 10-11am in the summer months). In future years, their root system will be larger and allow them to absorb much more water than it does now.

At temperatures above 85F, the leaves may wilt/droop as the leaves loose moisture faster than the leaves can absorb more water. But they should perk up on their own at night (if still wilted in the morning, water them right away). When I see them wilted and want to check the soil moisture, I insert a finger to a depth of 4" (most roots are in the top 4"). If the soil feels dry, I water them right away.

If you have an unusually bad wilting episode, the root ball may loose so much moisture that it begins to repel water. In those cases, a new planted shrub can be extracted and dropped into a large pail full of water until it stops throwing air bubbles (1-2 hours). Then plant it back. If it is a large hydrangea, that may not be practical so use drip irrigation or a soaker hose to water slowly, very, very slowly. You can also use a regular hose as long as you set it to water very slowly.