If your child is holding it in all day only to explode in their underwear somewhere, they usually have bathroom anxiety, or just more comfortable hiding behind the couch.
If you drop your child to daycare or grandma’s house during the day, make sure that you walk them in the first time and get them comfortable with the bathroom and the toilet. I recommend you let your child see you use the bathroom to lessen their bathroom anxiety. Then let them sit and make before you leave. So, they should be good for a while, and not scared of a strange bathroom. Make sure their caretaker knows that you are in potty training mode, and should be checking on your child every 30 minutes to see if they are ready to try again.
If your child is still holding it in all day, even when your home, buy them a special prize to combat their bathroom anxiety. Something your child really wants. Let them pick it, and put it on the kitchen table. Tell them they can only play with their new toy after they make on the toilet. Plus, they can only play with it for 5 minutes, and then it’s back on the table. I’ve seen this work. The child is dying to play with the toy again and will go to the bathroom just to gain a few more minutes with their new prized possession. This also works if your child likes playing on your phone. Download a new app, and follow the same rules as above.