The latter - 10 minutes max if you have all the data and the paper load sheet you need. Maybe the a/c libary was incomplete and no-one had 'topped up' the load sheet folder? Getting to a phone and having one faxed etc etc could just add up to 2 hours. Maybe dispatch was inefficient? Maybe holds/pax were loaded incorrectly? Also not too difficult to write a PDA/Laptop spreadsheet version to double-check your paper answer. The best solution is to persuade the company to introduce a 'Nil Change of Load' load sheet for such diversions. That takes about 3 minutes to complete.
2 hours could also sound like "get the book out Fred - how do you do these". If the crew are 'regular' scheduled fliers with computer load sheets at every destination they would be well out of practice.