Donald Trump begins his official work day as late as 11am and is known to clock off at 6pm, leaked copies of his private schedule reportedly reveal.

The US president often has ill-defined "executive time" scheduled in the early morning and at other points in the day, according to the political website Axios.

The periods are used for Trump to make phone calls, watch television and send tweets, it was claimed – often from his private residence in the White House.

The late official start contrasts with Trump's early months in the White House and with previous presidents.

George W Bush typically arrived in the Oval Office by 6.45am while Barack Obama would work out before holding meetings from 9am or 10am.

A White House spokesman defended Trump as "one of the hardest workers I have ever seen" and said he works when in the residence.

Trump has 'executive time' set aside - time he uses to watch TV and tweet. (Photo / AP)

The report emerged amid separate claims that White House lawyers are now preparing for Trump to be interviewed by the official investigation into Russian election meddling.

Trump's legal team is anticipating that Robert Mueller, the special counsel leading the investigation, will ask to interview him, according to NBC News.

The broadcaster said there were discussions about whether Trump should give written response to questions or take part in a sit down interview.

Mueller is looking into the Trump campaign's communications with the Russians before the 2016 vote as well as wider concerns about election meddling.

Trump's work practices and mental health have entered the spotlight after a controversial book about his White House called Fire and Fury.

The book, written by journalist Michael Wolff, claimed that "100 per cent" of Trump's senior aides conclude he was "incapable of functioning in his job".

On Sunday, it was reported that Trump sometimes does not have his first formal meeting until 11am – often an intelligence briefing – and his schedule can end at 6pm.

Before 11am and scattered throughout the day are periods of "executive time", according to a report by Axios. His official working day is longer when travelling.

White House press secretary Sarah Huckabee Sanders has defended Trump, saying he's one of the hardest workers she knows. (Photo / AP)

Sarah Huckabee Sanders, the White House press secretary, said: "The time in the morning is a mix of residence time and Oval Office time but he always has calls with staff, Hill members, cabinet members and foreign leaders during this time.

"The President is one of the hardest workers I've ever seen and puts in long hours and long days nearly every day of the week all year long. It has been noted by reporters many times that they wish he would slow down because they sometimes have trouble keeping up with him."

The timings chime with other US media reports. The New York Times has reported that Trump spends four hours, or sometime even double, in front of a television each day, often on cable news channels.

Wolff's book claims that Trump can be in bed by 6.30pm with a cheeseburger watching television and making calls.

There have also been numerous reports of Trump spending the morning and evening hours phoning old friends and associates outside politics, as well as sending tweets which often appear to spin off from cable news.

The White House has denounced Wolff's book in the strongest terms, dubbing it "trashy tabloid fiction".