As the GM I will usually post two or more times a day. I also expect players to post at least daily and preferably twice. If you have abilities that interrupt others actions (like
Step Up) plan on posting more often. Those players who do post more often (within reason now, let's not get carried away) will likely be more prominent in the campaign.
There will of course be exceptions caused by real life, but I will not hesitate to let your character get “left behind” or “lost” and “found” later if necessary - what occurs in the meantime will vary depending on the player’s attitude and consideration for others. If you know you are going to be gone, just let me know and we'll work around it. If you are repeatedly absent, I may ask you to step away from the table.
If your character is absent during combat or you're otherwise holding the group up, I will delay your action, or chose an appropriate action for you - whatever seems to make the most sense. I will try to leave time for folks to catch up - I know we all have other responsibilities.