If in a hot soil, like ocean forest, water only for now and the next month ish. It something lighter, like Coco or a coco mix like light warrior. You can begin the seedling feed immediately. But only feed with the Bergman’s 2-3 times a week in soil. At peak. So you alternate feed/water only/feed/water only. If using something like happy frog you can start the seedling feed at about 50% immediately. And you are correct. Not worth making a whole gallon of it.
If in a 100% innert medium, like straight Coco coir, you feed full strength every single day. Honestly if you are using ffhf or ffof you won’t actually ever need to even open the seedling feed. Think thats about the best way I can break it down with provided information. Here is a more detailed breakdown too.