Varies with the plants. Some wilt and don't recover overnight. Others take on a "miscolor." Lawns may turn a touch purple or grey before turning brown. Deciduous plants often grey a bit..it is subtle, watch for it. Some plants will begin to roll their leaves in an attempt to reduce surface facing the sun. Damage begins such as burned leaf edges or flower buds falling off.

Insect problems such as spider mites literally explode in hot, dry weather. Leaves will feel gritty, have stippling marks from feeding.......and eventually webs form. By the web time the infestation is severe.

Mulch, mulch, mulch to conserve any moisture.

Damage may not appear until next year as the plants are not making enough carbohydrates for good growth and flowering next year.

In other words, it varies with the plants.