Honestly, at that age, I'd have someone else to look after him while I worked. Even if it's only for an hour. Even an older child just to play with him or hlep him if he needed help.
At 3 y/o, none of my kids had a good grasp of how long an hour was, and, while an older child might understand not to interrupt mom unless there was an emergency, an "emergency" for a 3 y/o might mean he needs more juice, yk?
As for missing learning moments--that happens. Lots of times, something comes up while I'm driving and by the time we get to where we can look it up, the interest has passed. If the topic is something that really interests your ds, then waiting an hour won't change that. Many topics of interest have been revisited here months, even years after that first spark. I wouldn't worry about that.
Single Mom to 3 (12, 17 & 21) and .