In order to do this I have to select photos for specific day and there's no way to do it. On my computer these old photos are in directories named with date, one directory per day, but in Google Photos this information is lost, they are entirely random (these photos really have random dates, camera clock was randomizing each time I switched it on).

Simple script would solve that but Google Photos has no public API because public APIs are so 2006. There's no way to reupload photos with fixed EXIFs too.