K-dog you are most welcome!
As for duration? Well, take some concrete measurements of your current flexibility, then give it a month of consistency and see if you've made gains. If there have been ZERO gains after a month, then I'd say you have something else going on restricting the length ... neural tension or a fascial restriction.
And the research I remember (I can dig it out if you want the reference ... it was done by one of my profs) stated 2-4 reps of 30 seconds in one session. I am not sure if you'd get the same effect spreading it out over the day.
Something to consider is tissue readiness ... after a workout, the blood flow and tissue warm are optimal for increasing muscle length ... after you've been sitting for 6 hours in a 68 degree office ... maybe not so much. Does that mean that you shouldn't stretch after sitting for 6 hours? No ... it means maybe you should do both!
Bill, good points ... thanks for the reminder!!