After transitioning to the NG next summer to reclassify as an 11B after I EAS, how long do I have before I need to attend IBOLC?

Please clarify. You said you are going to reclass as an 11B. That is an enlisted MOS. The code for an Infantry officer is 11A. So for IBOLC it really depends on how backed up they are and when they can get the slot. As for grad school, if you are close to finishfin, that would be more doable than just starting the program. But if you are in an Infantry officer position and not through IBOLC you are non-MOS qualified and the command gets graded on that.

My experience is decades old, but if you look around at the Brigade, or even Battalion, level you might find a Signal billet that you could move into rather than having to reclass as Infantry. You may have to travel a bit, but it would match your current skills more directly. Though for the life of me, I personally can not understand anyone wanting to wear anything but the blue chord and crossed rifles. :-)

What is your current Branch in the Marines, or however they classify Officer Jobs? When I switched Branches as an Army Infantry Officer as a 1LT, I did not go back and do the Engineer Basic Course, I did the Engineer Officers Advanced Course, what would now be the Captains Career Course. At that time, as a Guard Officer, you could do that course with two shorter active phases and then distance learning for the rest. I would think that would be what they do for you since you can't promote without being "Fully Qualified" , which as a first 1LT could push you real close to that second promotion board as not qualified.