I do every show this way, for a variety of reasons. Many of my shows, I hand off to another stage manager - so the clarity of the calling script is very important to me. I also tech VERY, VERY fast - and use the time of typing in my cues to review and clean up the teching. (I tech with pencil and paper, and then review by typing in the cues.) Also, a lot of the productions I do have a possible remount, co-production or future production attached . . . so I like have a very clear copy of my calling script. PLUS, I have a back-up copy of the calling script (How many stage managers do you know NEVER COPY or have a back up copy of their calling script?)
I find it very effective to me. I usually come in an hour early during tech, and type cues from the day or tech period before. (I just like being in the building, and fielding questions, so by doing this I have something to do.) It also allows me to snag designers and any questions I may have.
Like I said, I do it for all my shows, they run 5 weeks - 10 weeks.
I use WORD - using arrows, shapes and call-outs. Once the script is typed in (usually do during pre-production, if it is not in word already), I find it takes 4 - 8 hours to type in all the cues depending on the complexity of the tech.