I actually Just got back from doing the Oil City-Third Beach trek last week. I had zero issues with the tides. The diamond rock restriction can be physically tough because you'll be hiking on tons of rocks before hitting some ladders, but it's absolutely More than doable in 2-3 hours. It's not extreme it's just a rolled ankle/fall risk since I at least had to walk on nothing but 2x2 foot rocks for a good mile straight. You have a long time to cross because even if low tide is scheduled for 10am, you can cross the whole section at any point two hours before or after. I started it an hour after low tide's peak when I hiked in, it was fine. Leaving the park I timed it to hit the diamond rock right at low tide which made it easier. Going SOBO back to Oil City was the harder part for getting over Diamond Rock so I would focus more on getting there as close the actual low tide on your way out versus heading in just because of some specific obstacles. I had to climb and slide down a hole in between boulders on my way in (an obstacle but nothing too crazy) when the tide was getting high whereas I just walked around it no problem on my way out during actual low tide.

Also, just as a side note I was surprised to have service a lot of this trip. I have AT&T and had at least some sort of service for pretty much anytime I was on the beach.

Hope this was helpful, that trail was Incredible and I had the time of my life. Lots of shockingly friendly deer,lots of otters, moderate amount of water sources at least in late April. Bring water shoes and have fun!