Make sure you book it as your first LL selection on Genie+ and you won't have a problem getting on. If you're able to enter from international gateway (either an Epcot area resort or a Skyliner resort), arrive at the gates about 45 minutes to an hour before early entry starts and you'll be able to be one of the first on the ride for the day.
We did.
Exactly at 7am I would have booked Rat, but it was coming up grey, as if the ride was down for the day. I immediately chose Frozen. Next, I immediately attempted to modify the Frozen pass. Rat showed up as an option.
Here's where things get murky. I am 99% certain Rat showed up as available for
9am. I immediately chose it, and quickly clicked through the screens. (I did not carefully double check the last screen. I saw the 9, and clicked confirm.)
At 9am, we walked up to Rat, only to discover that our actual return time was
9pm, on a day when Epcot closed at 9:30pm. (odd) When booking a G+ pass, especially early in the morning, there can be a big time jump between the first screen and 3rd screen. Other days of the trip we also saw big time shifts, not as dramatic as that day, but dramatic.
Unfortunately, we had to leave Epcot before 9pm, so we could not use the pass. We went to GS and plead our case, but they were not sympathetic. I don't think they believed me or something. They saw we had gotten a BG for GoG (used multiple phones) and basically threw that back in our faces. "You got a BG for GoG, many people do not get one." It was weird.
The only option they were willing to offer us was to let us have the Frozen pass back, for roughly the same time we'd originally booked. We begrudgingly took their offer. The plus being that our Frozen pass was for 9am. So we used it right away, then we were able to book another pass.
On that day, Rat passes were all gone within minutes. (I did check that.) At 9:05am, just after regular park opening, Rat standby was already up to 75minutes and building.
If OP's rip is Easter week, then Rat passes might be gone as quickly as the week we visited. I'm sure that is not the case all eyar,but peak weeks
MDE can glitch at 7am, and Rat ca be gone very quickly.
Other days, we also had problems with MDE glitching on us at 7am.