I actually believe your next G+ is 2 hours after AK official opening, since that's your first park of the day, but I won't swear to it! I know we've done it in the past, and I thought the first park is the key. But as soon as you make your Remy LL, the
MDE app will clearly show you at the top when you are eligible to book your next LL.
You're probably already aware, but your Remy "later in the day" could take a little modifying. Since you'll get the next available time, you might need to monitor and modify the time later.
Are you driving or using Disney transportation? Depending how things go at AK, getting to HS by 8:45 could be ambitious, but maybe not! But whether driving or busing, there could be some travel/wait time in there. Busy day!! Enjoy.