This question is related to a similar question asked before. However, it focuses more on a specific detail.
From time to time I have to talk to a colleague face to face. So I go to their office, knock the door (despite it is usually open) to make them aware I am there and then wait for them to look at me. The time until this happens can sometimes be awkwardly long (although it is only a few seconds). I have no problem with this, though.
The reason I usually wait until they look at me is to make sure they can finish their current thought and can decide for themselves when to interrupt and talk to me. I, personally, would like people to e.g. let me finish my current typing so that afterwards I better know where I left off. However, more than once I got the feeling this waiting annoys people. Often they already ask me to start talking to them while they are still concentrating on their monitor and are typing.
Should I start talking to them immediately or should I wait for their full attention?
For the sake of this question lets assume that asynchronous communication like writing an E-Mail is not an option.