There's nothing in the photo that gives relative size, so it's difficult for me to imagine it as a smeared cecotrope. Honestly, it looks like the size of a dog poop, haha, but I know it's not, so I'm forcing myself to assess just based on the visible color and texture.
The hay addition is really good and is really going to help get healthy bacteria into and consistent within their stomachs. When you go to the rabbit vet, I recommend having them look at their teeth -- one of the important functions of hay is that it is actually sandpaper for rabbit teeth. Rabbit teeth never stop growing (like human finger nails), and hay/grass is actually textured in small blades, not smooth to the touch. To eat hay/grass, rabbits really chew the heck out of it, and that keeps their teeth from growing out in painful ways in their mouth. In a baffle of evolution, rabbit back teeth can grow spikes inwards, towards their tongue, and also outwards, towards their inner cheeks. Not having hay for that long makes me wonder if their teeth are ok.
..... I think really trying to keep both your rabbits hydrated and get them to eat as much hay as possible is a really good step until Saturday. There's a chance they won't eat a lot because 1) hay isn't as good as pellets for most rabbits, taste-wise and/or 2) it may be uncomfortable to eat it if they have dental problems already. Don't introduce any veggies or new foods - your instinct on that was really good. Different bacteria are needed in the gut to break down different foods, so it's important to get your rabbits' stomachs more settled with hay first. Again, the poop seems to be a good signal that there is an upset tummy in the mix. Hay gives lots of fiber, and that will hopefully get the poop to become more solid. Since it's so loose and wet, they may be losing a lot of water, so hydration is important.
If they allow you to get close, can you listen to their stomachs (just smoosh your ear against their side)? If you hear lots of gurgling (like if you had an upset stomach and felt gas moving around), you can buy simethicone, aka infant gas drops at a local pharmacy or something. It is safe to give plain baby gas drops to rabbits (they can't overdose on it), and it helps move gas through the system so it's more comfortable for them. This is usually more helpful for episodes of gas, rather than treating a chronic stomach imbalance, but if your rabbits are going through a gas episode now as a result, this can provide some relief. Simethicone usually comes in a bottle with a dropper. I usually just give a full dropper, and the rule of thumb is one dropper for 3 hours, and if you don't see improvement, it probably won't help with future doses.
If possible, I would talk to the vet you spoke to and ask for his/her recommendations as well. If she/he has an e-mail, maybe send the picture and ask about their recommendations, as of now.