From the information,it looks like the actual mark-up will take sometime & should be initiated in the Senate immigration sub-committee in late-May,but knowing the Senate I'd bet ~mid-late June for the actual mark-up & it would also explain a possible ~September vote.

On your last question,this is why I believe they are not really serious about tackling immigration since I'm pretty sure they know what to expect after it has failed the last 2 times.