I use bellwork at the beginning of my class to help get students focused and also to work on skills that students need. The last few years I have been planning out the questions at least a week ahead. 7th and 8th grade have themes for each day (different, except for Friday), but for Wednesday, I review where we are at in content and have a question that directly relates to content. I have a Google spreadsheet with a general plan for video links I use on Friday, links for listening comprehension clips that I use on Thursdays, I have a file of picture puzzles I use on Monday, graph sources, and etc. I have typed up and modified appropriate level readings from "Data Nuggets" for students to read and then use that information to respond/populate graphing information. So, most of the year is planned out.
On Fridays, I type up my questions and copy them into three columns in a Word Document (this can be done in a Google Doc, but is more complicated) and have these cut out for students to glue into their notebooks on Monday. I also use Blogger to post the questions for each class. Usually, the questions are the same for a section, but if one section is enough different than the other sections, I will adjust on the blog and students can see that. I think it's been helpful to have a slightly different focus in bellwork and then getting into content. If OpenSciEd works out like I am hoping, in the future, I may make adjustments to what I do for bellwork. Right now, this works to have things mostly planned, while still being able to be responsive to student needs and overall pacing.