Breaking news as we come on the air tonight, we are just hours away from a possible ceasefire between Israel and Hamas. Israeli forces still bombarding Gaza with airstrikes in the final moments leading up to that four day pause, expected to start at midnight Eastern Standard Time. The wait for the families is agonizing, plagued by uncertainty, unsure if their loved ones will be among the 50 hostages released over four days. 13 women and children expected to be among those freed Friday morning. Hamas will get 39 Palestinian prisoners as part of the deal. Meanwhile, the Israeli military has detained the chief of Gaza's largest hospital over what it claims is evidence that proves Hamas has been operating a command center there. Our team with a firsthand look inside the sprawling tunnel complex as that midnight deadline approaches. Israel cautions the situation is fluid, and anything could happen even at the last minute. ABC's Matt Gutman leads us off tonight from Israel.

Tonight, the biggest diplomatic breakthrough since the October 7 terror attack on Israel. At midnight tonight, a four day ceasefire between Israel and Hamas is set to begin, followed by the release of a total of 50 hostages. The US, Egypt, and Qatar brokering the deal to release 13 women and children held by Hamas. At 09:00 a.m. Tomorrow, Hamas will get 39 Palestinian prisoners. Qatar saying the hostages will be handed over to the Red Cross before being transferred to the Israeli military.

All women and children and those hostages who are from the same families will be put together within the same patch.

And Israel tonight guarded Sal Mam Shikhli Lahem Gamma, its chief military spokesman, warning that nothing is final until the exchange actually happens. And for the families of the hostages, the wait is agony, especially for those who know their children are not on the list. People like Ruby Hen, his son. Itai was taken from an IDF base on October 7.

Now that we're so close to that hostage deal, how does it feel as a father of a soldier, a male soldier, who knows that their child is likely not coming back tomorrow?

Yeah, so it's twofold, one. I have established a new family of 240 new family members that each one of us are together. And I'm sure, Matt, when you have a family member that is celebrating some sort of event, you need to be joyful for him. But this framework needs to be continued to the next leg. And the next leg should not happen a year from now, needs to happen soon.

And once it begins, desperately needed aid is expected to start flowing in from the Rafa border into a decimated Gaza. And in the final hours before this ceasefire, israeli forces pounding Gaza. On Wednesday, we traveled to Al Shifa Hospital, gaza's largest.

That's the hospital right there. That's the Al Shifa hospital directly across from us.

That UN bus loaded with patients and displaced people evacuating the hospital. The director of Al shifa later pulled off one of those busses and detained. Israel's security service said it questioned him about the weapons caches they found and tunnels running beneath the hospital's largest building. The IDF, which screened our footage for security purposes, taking us into one of those tunnels on Wednesday right beneath the complex's largest building. Drop in.

It's pretty tight in here, but you can see right up here, looks like there are pipes for an air vent.

Walking through a portion about 150 yards long.

This appears to be a kitchenette. You can see it's even tiled here.

There is a sink, even what the IDF called a dormitory.

I mean, is this part of the hospital?

This is not the part of the hospital.

It looks like the tile from the hospital.

It is not the hospital. This is the way for them to use the hospital as a human ship.

We saw no evidence of a command and control complex, but tonight, the IDF releasing new video of a drone flying through the entirety of that tunnel, then flying up and showing the two entrances in the hospital complex. Do you think that you found what you expected to find here at the hospital?

Yeah, because what was important for us is to understand the system.

So let's get right to Matt Gutman now, who joins us from Tel Aviv live. Matt, you have new reporting about how this hostage release is expected to play out. What can you tell us?

Lindsay first, the hostages will be ferried by the Red Cross from Gaza into Israel. At that point, they'll be met by a specifically trained Israeli military unit that will verify their identification. At that point, for the first time in 49 days, they will be able to call their loved ones. Then they'll be checked medically. They'll also be debriefed by Israeli intelligence officers. And after about 2 hours or so, they'll be transferred to hospitals in Israel, where they'll finally be able to actually hold their loved ones for the first time.

Again, Lindsay, those families on pins and needles tonight. Matt, thank you.

Hi, everyone. George Stephanopoulos here. Thanks for checking out the ABC News YouTube channel. If you'd like to get more videos, show highlights, and watch live event coverage, click on the right over here to subscribe to our channel. And don't forget to download the ABC News app for breaking news alerts. Thanks for watching.