"If it really was zero across the board on tariff protection, I think other suppliers than the United States would ship most of the additional cars to China", said Gary Hufbauer, a senior fellow at the Peterson Institute for International Economics.
Earlier on Tuesday, Treasury Secretary Steven Mnuchin also raised the prospect of the deadline extension.
Late Sunday, Trump tweeted that "China has agreed to reduce and remove tariffs on cars coming into China from the U.S. now the tariff is 40 percent".
Meanwhile, as Trump and White House officials tout the truce, Beijing has said little on a pact that cheered markets but left many questions unanswered.
For meetings such as the Trump-Xi dinner, the initial official news report is typically drafted by the foreign ministry and approved by the General Office of the ruling Communist Party's Central Committee, she said.
The changes USA officials have sought include forcing Beijing to lower tariffs on USA goods, stop dumping cheap steel and aluminium into foreign markets, and halting the theft of intellectual property, among other things.
The White House said talks would take place to resolve within the next 90 days specific USA complaints such as forced technology transfer, or else existing 10 percent tariffs would go up to 25 percent.
Trump said he and Xi "are the only two people that can bring about massive and very positive change, on trade and far beyond, between our two great Nations".
Both sides will immediately hold talks on structural changes concerning forced technology transfers made by Chinese firms on US companies, intellectual property rights protection, non-tariff trade barriers, cyber intrusion concerns, cyber theft and agricultural, the White House added.
Larry Kudlow, the White House's top economic adviser, said he couldn't speak to the reason why Beijing didn't include a timeframe in its own statement following the leader's dinner.
White House trade director Peter Navarro detailed on Monday what the administration hopes to accomplish by lifting tariffs on China for 90 days. However, at least one major Chinese state media outlet mentioned it on its account on Chinese social media platform WeChat, referring to the White House statement.
China, for its part, also agreed to offset its massive trade imbalance with the U.S.by buying more, but not yet specified amounts, of energy products, agricultural, industrial and other products. "MAKE AMERICA RICH AGAIN", he continued.
Per China, "Trump said the USA side welcomes Chinese students to study in his country".
"However I will give it to him that he has managed to bring China to the table", said Guajardo, who is now a senior director at Washington-based McLarty Associates focusing on worldwide trade.
That was a very different message to the one that emerged immediately after the dinner, when Trump said that he and Xi had agreed on "an incredible deal" and that US-China relations had taken a "big leap forward".
Some industry participants expected China to drop the tariffs soon after the Trump-Xi meeting.
"He's constantly invoking the stock exchange as a referendum on his presidency", Guajardo said.
Here's what we do know: if both sides keep to their word, there won't be any new tariffs being lobbed around in the next few months.