I started my own personal challenge about 3 weeks ago to sit for atleast one half hour daily of just straight anapana sati, i focus on the point where the breath-contact is felt, i didnt realize there was a meditation challenge here this whole time until just a few days ago.
This past 21 days consecutive sitting for at least 30 minutes has been wonderful. usually i sit for a half hour here, 20 minutes there each day, almost an hour daily! my work schedule is never the same so i am not free during the same hours routinely, although if i am assigned to work where/when it is slow, i do standing meditation, or when im not actively engaged, i will meditate in whichever way the body is disposed.
I am challenging myself to sit for at least a half-hour daily, gradually increasing as needed. two suttas im constantly reflecting on in my practice is "nodding" or "dozing" Pacala Sutta in the Anguttara Nikaya (access to insight says 7.58, but the book i have says 7.61)
and also Vitakkasanthana Sutta (removal of distracting thoughts) Majjhima Nikaya 20.
i think i will keep it up, im actually enjoying more than i do ordinary worldly things, im starting to look foward to it, it is a most enjoyable practice to me.
I have insight timer, and found/joined the dhammawheel meditation challenge group but havent posted anything there yet.