Dhutanga translated as "renunciation" is traditionally a set of 13 practices forest monk in Thailand undertook when wanting to energize their practice:
For us, this is an opportunity to design a practice that fits our individual needs, like committing ourselves to go through the day (we can even set our own start and end times) to refrain from smoking, to eat vegetarian only, to refrain from eating after lunch, to reduce our sleep time by one or two hours, to do 14,000 steps on the pedometer, to spend an hour more at the gym, to conduct a mindful, lovingkindness conversation with a stranger or a family member for 30 minutes, to spend an hour helping a friend without compensation, to walk mindfully for 5 minutes five times, etc. The possibilities are endless.
Once you have a goal, commit yourself to doing it on a Dhutanga Day, RSVP to signify your intention and do it.
We don't have to tell anybody what we've committed ourselves to doing. It's for us alone. If you wish, you can intend to share the merit i.e the positive outcome if any of your activity to all living beings, to your spouse, to your enemy, etc. The Boddhisattva attitude can add force of commitment to your intent.
If you do undertake the practice, feel free to share your experience at Sharing on Thursdays.
RSVP signifies your intent to undertake fasting on your own. Nothing more.
You may start the night before after dinner if you eat dinner, say, at 6 PM and end it at 6 AM on Thursday morning. Or you may start upon waking up on Wednesday morning and end upon waking up on Thursday. Create your own practice.