You are better off with your daily Genshin routine or whichever routine you follow in the game. It's not necessary to follow a scheduled grinding routine to raise the Friendship levels because eventually, you will achieve them. There are plenty of sources to obtain the experience in the game, and slowly you will obtain the levels. I feel that you should keep investing in your characters, and as you are spending resin on usual activities, the experience is getting accumulated to your characters. This is what I've followed from time to time while keeping the team firepower in check. If there's a boss that requires me to use invested characters, then I switch to them. Otherwise, I keep one or two unbuild characters in the team to pump some EXP to them. Another passive way to generate Companionship EXP for your characters is to place them in the Serenitea pot where you can accumulate EXP for them. You have to place them in your Pot where they will get experience, and you will be able to raise your characters' Friendship levels. Additionally, you can co-op with others to get double the Companionship EXP so that you can raise your character's Friendship levels faster. Ultimately, it depends on your time management and schedules with the game. But, I've given a few tips that I would have followed if I was in your shoes. Personally, I co-op with a lot of my friends and sometimes random people to help them out or take help from them.