Yes, 25 is the magic number. But this isn’t quite correct because the learning order matters. To get that 7 day/level speed, you absolutely need to learn all radicals on that first day. When all those radicals guru 3.5 days later, you need to then immediately learn the remaining kanji that become unlocked. By that 3.5 day mark you should have all available kanji learned. Then (hopefully) 3.5 days later you have guru’d at least 90% of the kanji for that level.
If you’re not using the lesson picker, then the maximum number of lessons you could do per day is 30. Then, based off of the new algorithm described here, the question is “for a given level, is there a number of lessons less than or equal to 30 that will ensure you learn all radicals immediately on the first day of that level?”
It will take a little bit of investigating to answer that question.