Hi Sarah
That is very exciting. But you are right not to keep lifting the lid, in case it’s a female. But it also may be a male using it for a short stay. They do sometimes decide to spend the day in a feed box. I had two during the really hot weather who seemed to take it in turns. I suppose they must have thought it was cooler in there. I imagine if a hog is planning a longer stay, it will take more nesting material in, so you may get an idea of what is happening. The hogs here who have made a nest usually leave a little trail of vegetation into the doorway. If they are making a nest you will have to put the food somewhere else. I had to have a new feed box last autumn when a hog decided to build a nest in the original one!
I’m guessing you don’t have a camera? You could quietly put something, such as a twig or a ball of paper, in the doorway so that you can see if the hog comes out, but of course won’t know if it goes back in. To be safe, I would just leave the food nearby so that the hogs still find it, but try not to disturb the box. Keep an eye on it to see if you can work out what is happening.
Good luck.