I'm *very* leery of completely covering anything with a bag (especially one that lets the light in). You create an ideal environment for mold & rot here in Florida; moisture can't evaporate and you have no airflow. My first year of mango obsession I followed the advice for starting mango seeds on a webpage written by someone who lived out West (not on here/TFF); they instructed that you cover each pot with clear kitchen wrap and a rubberband to keep it on tight. I started probably 3 dozen freshly harvested turpentine seeds, after three weeks of nothing, I pulled the plastic off and discovered each seed at some stage of rot. A few weren't completely rotted, I cleaned them and replanted without covering and each sprouted.
I use parafilm/buddy tape and a few clothespins on the graft union now, no covering beyond that. I do agree it's probably helpful to protect/shade the graft itself during these hottest months with the most intense sun, but I usually just move the pot into partial shade or rotate it. Obviously, you need to expose the new growth to direct sunlight gradually (if it was shaded). Direct morning sun is ideal, then after a week or so I'll move it to a more sunny location. You'll risk sunburning the leaves if you don't put a little thought into how you do it.
One counter observation to all the extra care, on in-ground trees with grafts in direct/full sun, I treat grafts the exact same (tape & clothespin) and never had a problem with takes or burns.