I'm creating a course that has a number of exercises or assignments for students to do on their own time (i.e. untimed). I'm not sure if it's best to do this as a "Lecture" or as an "Assignment". What I like about the "Assignment" is that it allows students to submit their experiences to me privately. What I don't like about it is that it requires me to provide a "solution" (which, in my case, is not really appropriate since the exercises are experiential, so there's no "right" answer) and also that it requires me to put down an "estimated duration". In some cases, these might take only a few minutes, but in others, they are practices that the student should engage in over the course of days or weeks.
Also, all of the assignments are optional. So while I want students to be able to submit their experiences, not doing so shouldn't prevent them from advancing through the course.
I had the same issues. I am assigning management tasks I want them to do with their teams. The idea of either duration or solution is not relevant. So I do them as lectures that I label "Assignment #1" etc. I only ask them to send them to me at the end of the course as a portfolio of exercises. Of course, it is optional.