If hes overly optimising or not paying attention that should be corrected or slapped down by the DM IMO.
If he's just 'worried about getting it wrong' then he needs to be told that there is no right or wrong option; he should just look at the battle through the eyes of his character and make a snap decision accordingly. Some times itll be optimal, sometime it wont. Sometimes it wont be optimal intentionally (he may elect to dodge becuase his character is scared, when the optimal thing to do would be wildly different).
If he doesnt declare in three seconds he takes the dodge action. In other words, the only wrong decision is not making a decision within three seconds.
Im extrapolating here, but it sounds like he's playing with a group who are more optimisation savy than him. I usually see this phenomena in this situation. Players hesitaite when they are too scared to make the 'wrong' decision in order to avoid drawing the scorn or dissaproval of the other players (and occasionally from the DM).
If this is the case its a much more serious issue, and I would definately have a chat with him about it.
I could be way off and he could have a serious anxiety disorder though.