Anyone knows of any tingkat service which allows us to choose only 3 times a week instead of the usual 5 days?

You can consider this: http://sg.foodmatters.me/subscribe This allows you to choose how many meals in a month you would like, minimum is 4 meals per month. If you want 3 times a week, you can choose the "Light" option for 12 meal credits a month. Unfortunately, this is not exactly "tingkat" and they only do lunch time delivery now. Not sure if this will be suitable for you. One other tingkat service I've found is Mom's Cooking (http://www.momscooking.com.sg/pricing/) which offers a 4 day option.

Maybe you consider FitThree? It's not exactly tingkat meals but it is packaged in recyclable containers and the meals are catered to be healthy and especially for those who are on a diet or working out. They offer a 3 day meal plan as well as a 5 day one. I've actually tried some of the meals (swiped them off a friend who orders regularly from FitThree) and they are pretty good. https://www.fitthree.com/howitworks