Are you solo? If so, it is very easy to single rider EE if need be. I've never waited more than 10 or 15 minutes in the single rider line. I would be trying to refresh and switch my Navi to FOP from the minute I entered the park that morning- we had luck with getting FOP the day of on our trip a couple of weeks ago. We were 3 people, so if you are solo then you have an even better chance of pulling a FOP the day of while in the park. Navi likely will have a shorter line than FOP- so if you have to stand in line for one then that is the better option if you get lucky and can pull a FOP time. For now, my plan would be to keep the Navi and try to get 2 other FPs burned as soon as I could when I got there. That way once you scan into Navi your 3 are done and you can try to get another Tier 1, so you can keep trying for FOP. We picked up a FOP by trying during the afternoon hours (well technically I was trying for Navi- but an FOP time popped up so we grabbed it) and got to ride it a second time as we had a FP+ for it booked 60 days before our trip. Even if you don't want to do the things you get your Tier 2 FP for, you can go over and scan in and then not do them. As long as you scan- you can burn your Tier 2- so you will be eligible for another Tier 1.
When we were there a couple of weeks ago FOP's line ranged from about 90 minutes to 180 minutes during the day. It had a big surge in the morning which was when it was 180, and then seemed to drop between 90 and 140 after that for most of the day-with it being 120 quite a bit. It was not a high crowd day. 10:00 a.m. was probably the time the line was the absolute longest for the entire day. So many people rush to FOP when they get to the park- even if the line has already build up, that that line is long in the mornings. WE saw that with Slinky Dog too-- 10:00 a.m. seemed to be the peak for the longest lines- at least during our trip days.
As EE is important, if you get into the park before 10:00 a.m., I would immediately begin trying to move my EE FP up to the current time and ride it. Then I would be looking for an available FP anywhere for any Tier 2 attraction. I would either go ride/do that Tier 2, or just scan in. (My goal would be to get to EE soon enough even if it is during your set FP time that you have a big enough window to get another Tier 2 booked before your noon Navi). Then, I would scan in at Navi at 11:55 (you can scan in 5 minutes early) and then as you are now eligible for another Tier 1 I would start trying over and over again for FOP. The best way to do it, is to book some FP+ (anything that is available doesn't have to be Tier 1- as long as you are eligible they will pop up on modify if available)-- I would do late in the afternoon or evening as you aren't going to use it-- then just keep trying over and over to modify it to get FOP. I would go straight from Navi to get in line for FOP no matter how long the line is, and I would use my time in line to keep refreshing to try to get FOP. Then you can either get out of line if you pull one, or use it to ride it again. We did Navi standby shortly after rope drop as our Tier 1 was for FOP- we waited 45 minutes for it as DD was slow that morning so we did not make it before rope drop. Unfortunately, the people behind us in the boat talked extremely loudly the whole time (and not about the ride-- about work and the Farmer's market etc) and they really ruined the ride- and not just for us, but for a teen that was put next to them in the boat as a single. He even asked them to be quiet at one point and the lady said "sorry" and then started talking again about 3 seconds later. So, I was trying to pull a FP+ to ride Navi again that afternoon after our FOP FP+--- I wound up getting an FOP FP+ to come up instead for an almost immediate ride, so we went and did that. I really wanted to ride Navi again so I kept trying and we got in line for it even thought it had a 60 minute wait. Right after we got in line, I was able to pull one that was only 45 minutes away, so we left the line. If you are solo, I would think you might get lucky at pulling a FP+ while you are there if you work at it.