(2-part post):
DSE? I started off thinking that was probably some sort of government department but couldn't work out which one so I tried a web search. This showed dozens of possible things which you could be referring to! So I'm only guessing when I post a reply based upon the possibility that you might mean 'display screen equipment':
There are no statutory limits on the time that you should be using display screen equipment for. There are also no statutory rules determining the length of breaks (other, of course, than the breaks which all employees are entitled to under the Working Hours Regulations).
This is from the website of the Health & Safety Executive:
"(2) The Regulations and guidance do not quantify the duration or intervals between breaks or changes of activity because:
(a) DSE jobs are very varied and what would be appropriate intervals for one job could be inadequate for another;
(b) Where circumstances permit, the best arrangement is for users to have some individual control over the pace of work and when to take breaks.
(3) [Recent HSE sponsored research (by Professor Cox et al, University of Nottingham), recommended amongst other things, that periods of work between breaks should be at least 50 minutes but not greater than 120 minutes, and that breaks should be between 12 and 15 minutes in duration. However, the researchers were only considering repetitive (short cycle) VDU work such as data entry, and their conclusions, which were subject to a number of caveats, are not valid for other kinds of DSE work.]"
Link:
http://www.hse.gov.uk/lau/lacs/16-1.htm