Every writer has their own style, methodology and schedule. Mine is ‘write when I can’ methodology, style and schedule. My style, I’m afraid, though realistic for my situation will not get me to where I want to be as a writer. Writing often keeps your mind sharp and in the writing ‘zone’. Being in the writing zone means whenever you sit down to write you almost instantly fall into rhythm. That is consistency. Writing when your schedule allows (for some, unavoidable) takes you out of the zone through inconsistency. The danger in falling out of the zone as a writer, it takes you awhile to recapture the story in your mind, ‘to get back in the zone’. This could affect the storyline in a negative way.
I know this first-hand. It is why I strive for consistency. To stay in the writing zone. Rather than let a week go by and then do a monster session to keep you on schedule, try to break it up into little pieces through the week that will keep you on schedule and more importantly keep ‘you in the zone’.