Students on all university courses in England will return "no earlier than 17 May", the government has announced.
About a million students, taking courses taught online since Christmas, will be able to go back to university campuses.
Since the start of the year, only students on hands-on courses have been allowed in-person teaching.
But the wait of another month to fully open was described as "hugely disappointing" by Universities UK.
Universities Minister Michelle Donelan, in a written statement, said the timing was a "cautious approach to the easing of restrictions" and "the movement of students across the country poses a risk for the transmission of the virus".
University leaders had been lobbying for all students to go back in April - saying it was unfair to keep restrictions on campuses when shops were open.
Students would be "bitterly disappointed" at the slow return to university, said Vanessa Wilson, leader of the University Alliance, describing it as "nonsensical".
The mid-May start is likely to raise further questions about refunds on tuition fees and rent, for a reduced term before the summer break.
Graham Galbraith, vice chancellor of the University of Portsmouth, said delaying for another month until after 17 May was "unfathomable".
"That this date is after many universities will have finished their teaching year shows a government with a cavalier disregard for details. This isn't good enough," he said.
"Students can now buy a book on British history in Waterstones and discuss it with a tattoo artist," - but they cannot go into a university and discuss it with their lecturer, said Prof Galbraith.
About half of students have been on courses only being taught online - but from next month all students will return to a mix of face-to-face and online classes.
Hillary Gyebi-Ababio, the National Union of Students' vice president, said: "We are pleased that the government has finally remembered that students exist."
But she warned that students would need support after so much disruption - including paying rent on accommodation they were not allowed to use.
The UCU lecturers' union, which opposed an earlier return, said it would be more "honest" to accept that many courses would stay online until the autumn.
"Restarting in-person activities in mid-May, with only weeks of the academic year left, makes absolutely no sense as most lectures and seminars will already have finished," said UCU leader, Jo Grady.
Students will be offered Covid testing on campus when they return - with an initial three tests under supervision, after which students will be asked to take tests at home.
There will also be an additional £15m for student hardship support this year, announced the universities minister.
In Wales, students returned this week, with a mix of face-to-face and online study.
In Scotland, some students have had in-person classes, but from 17 May universities will "return to a more blended model of learning". Although some universities in Scotland end their term in late May.
In Northern Ireland, hands-on courses have been taught in-person, but other courses are expected to remain online for the rest of the term.
'Forgotten' in lockdown
The 17 May timing aligns the return of students with the next phase of ending the lockdown - when pubs will open indoors and cinemas and theatres can open.
Unlike the mass return of England's school children in March, universities in England have had a patchwork return - prompting criticisms that students were "forgotten" in the plans for leaving lockdown.
Students on courses which required hands-on training, such as medicine and some sciences, had some face-to-face teaching last term.
But students on courses such as the arts, humanities, business and law had been waiting for a return date - which will now be about five months after they left for the Christmas holidays.
There are some other universities which have already decided to stay online for all this academic year.
Even without in-person teaching, many students seem to have gone back to their university accommodation - with a survey from the Higher Education Policy Institute suggesting about two thirds of students had been in their term-time addresses.
Labour's shadow universities minister, Matt Western, said: "Just a week before thousands were hoping to return to campus, they have been let down with yet another late announcement and no explanation of the reasons for this delay."