As U.S. officials and leaders in the Middle East are celebrating the proposed Gaza ceasefire deal between the Israeli government and Hamas but there are still many questions over the timeline and challenges to end the fighting and return the hostages that lie ahead before a deal to completely end the war is in place.

These include details of the deal’s timeline, and challenges to end the fighting and return the hostages.

The first phase of the deal, which is slated to be approved by the Israeli government on Thursday, will see all remaining hostages returned from Gaza, a number of Palestinian prisoners released from Israeli prisons and the partial withdrawal of the Israel Defense Forces inside the Gaza Strip.

It is expected that humanitarian aid will move quickly into Gaza once land crossings are opened back up.

A senior Israeli official told ABC News on Thursday that the 72-hour window for Hamas to release all hostages will begin after the Israeli government ratifies the deal.

The 20 hostages believed to still be alive are expected to be released all in one group on Sunday or Monday, the official said. President Donald Trump, speaking at a cabinet meeting at the White House on Thursday, said that the release of the hostages could be Monday or Tuesday.

Then, negotiators will move to the next phase of Trump’s 20-point peace plan, which was unveiled in late September.

Sources familiar with the negotiations told ABC News agreements still need to be reached on some of the most difficult points of the plan.

These include the total withdrawal of Israeli forces from the Gaza Strip, Hamas ceding control of Gaza, disarming and decommissioning the militant group’s weapons, and turning Gaza’s governance over to an international trusteeship overseen by the U.S. and Arab allies.

The challenges to implementing these terms are immense, according to sources with knowledge of the negotiations.

European and Arab allies plan to convene in Paris on Thursday for a Gaza “day after” meeting.

The meeting will focus on three main areas: security, governance and reconstruction. Conversations on Palestinian statehood will also be discussed, a French diplomatic source said.

Secretary of State Marco Rubio was initially considering participating in the Paris meeting, but he told reporters on Capitol Hill on Wednesday that he is not expected to attend the meeting due to the rapidly moving situation in the Middle East. Rubio made the statement before it was announced that the first phase of a ceasefire deal had been reached.

An administration official told ABC News that if President Trump heads to the Middle East this weekend, Rubio will be traveling with him.

ABC News’ Ivan Pereira contributed to this report.