Being an artist can be likened to being a athlete or a ballet dancer. You stop practicing, you get ‘out of shape’. I have had a busy few weeks of non-art but necessary obligations, and found that “I’ll skip drawing today” turned into nearly a month. When I did pick up a pencil, I could tell my skills had already dulled a bit. That is why I always carry two sketchbooks- a larger sized one and a literally pocket sized one that can be carried anywhere. I stopped by Grace church today, enjoyed the silence and peace, and did a quick twelve minute sketch of the pulpit. I feel better.
There is always time to draw. If you hone your skills a bit every day, they will improve much faster than if you just draw once a week. As noted elsewhere, you can also draw ‘in your head’ and draw from memory later – this is a fun exercise for the mind and brain. So even if you forget your sketchbook, always find time to draw.