Deadline extensions

A problem with assessment deadlines for complex pieces of work is that you can never tell in advance exactly how long the students will need to digest the material necessary to do the work. My case: A group work assignment (to build a Breakout game in JavaScript!) is taking the majority of my 200-student class longer than I estimated (I broke the game down into 6 stages for 8 teaching weeks + they had a mid-term "study week"). My original deadline is looming and I feel they would benefit from an extension over Christmas. However I said on Monday "Come to the Tuesday lecture and we'll talk about it." 22% of the class showed-up -- reasons for poor attendance were either Eid (a major Moslem festival) or (perhaps more likely!) a tough Java assignment deadline at 9PM that night. So I point-blank refused to give an extension (pique, mainly!) and postponed the decision until the following Tuesday's lecture ... It's aggravating! I don't like giving extensions as it feels like weakness (& a lot of large-group teaching is "front") and encourages students to expect an extension so they need not start working until the last minute. I also worry that giving an extension covering a holiday period will encourage plagiarism: "No lecturer support, so who else do I turn to? My buds!" We'll see what happens next week...