A couple weeks ago, I finished teaching a short course at Simon Fraser University in their Technical Communications program. The course is 100% online. As someone who has taught online but also someone who has been an online student, I can attest to the importance of the facilitators "presence" in the online classroom.
I was delighted when one of my students, in an anonymous feedback survey, reported that: "Having Rebecca's answers coming in at the speed of light on the questions posted on the discussion forum almost made working online 'better' than an actual classroom, where we typically wait an entire week to address issues."
The key to my success in this area is not spending a excessive amount of time logged in. During the week, I try to log into the course twice a day – at about lunch time and just before I turn off my computer for the evening. If I am busy, I skip the lunch time login. It is important to note that I'm in a time zone that is three hours later than my students, so my students are often up working later than I am. Each time I log in, I scan the discussion boards and post when necessary. Most of the time, there is no need for me to do anything, so I'm only logged in for 5 minutes. However, if a student is struggling I might need to spend 15-20 minutes answering their question.
Where my 'presence' is really felt is on the weekends. As most of my online students work full time, I appreciate that they spend most of their time working in the evenings and on the weekends. So, I make it a point to check into the course multiple times during the weekend, especially in the evening and on Sunday afternoon. These are the times that most of my students are working, so it is the time where I check in a little more frequently. Again, most of the time checking in involves a 5-minute check to ensure there is nothing new that I need to address. If I see something and I cannot address it right away, I acknowledge that I've seen it, and let them know when I plan to answer it.
My point is, that you do not need to be always there or spend an excessive amount of time facilitating to provide a sense of "speed of light" presence for your learners. You just need to acknowledge that you have seen their questions, and be there when they are!