Starting a sentence with "so" is actually an informal aspect of speech that annoys a lot of people! When used like this it's called a 'discourse marker', as is used to help direct the conversation. It doesn't necessarily mean anything. "So, I was walking through the park and saw a fox!" - the "so" serves no purpose other than to let the listener know you're about to say something. It can also serve other purposes, for example to relate what you're saying to a previous point, or to let the listener know that it's relevant, like your example "so if you can add your time zone to your profile, we can...". When used like this, it can sometimes be condescending: "So, if you could do this for me, that would be great" "So, if you had read my email, you'd know that we fired you yesterday"

usually we will say it to begin a sentence when we are thinking of what to say. it's like saying "um..", or "like.. eg "how was your weekend?" "so.. like, we went fishing and i caught a cod!" ^they are thinking of what to say. i think you can begin any sentence with so, as long as you are talking informally to someone. you can use it to start a conversation, especially if the previous topic is different to the one you now want to talk about. eg "so, how was your weekend?"

"So" is a meaningless sentence-filler.