The expected posting frequency is a minimum of once per day, ideally. Of course real life intervenes and our availability to post may get hampered once in a while, which is fine. If you know you'll be absent for a few days or more, please let us know in the discussion thread along with any instructions regarding how you'd like your character to be handled in your absence. If I know I'll be absent, I'll be sure to inform the group as well!
Out of combat, if a player has not posted within a 24 hour period, I'll assume their character remained silent and took no action, then I'll try to move things along as best I can depending on the situation. In some cases, if it helps move things along, I'll roll perception or other 'mandatory' rolls for the group (such as saves). When taking any action, if you believe a roll may be relevant, go ahead and include it in your post. If it applies, I'll definitely take it into account!