I've found that most students, counter-intuitively, don't actually write a whole lot more OR a whole lot better when given a great deal more time. A *little* more time, yes, especially when they're less experienced... but that benefit very quickly drops off. They still go for the three body paragraphs generally (not even the four they should be aiming for in the 60 min exam) and complexity of thought isn't magically conferred by having the luxury of moving more slowly. Parkinson's Law: the task we have expands or shrinks to fit the time we have to execute it.
I think a great deal of benefit in terms of inspiration is actually derived from having time-pressure, and it forces students to mentally edit their writing, before they commit it to page, to make it more specific, direct and succinct. Essays with very long time allocations often just have a lot of padding: say the same thing with more words. And the argument of inexperience doesn't work with having a quotation sheet brought in, either; you're not inexperienced in just memorising stuff.
So, personally, I'm not in favour of going soft. People tend to meet the expectations placed on them; we are expected to be slow and bad, we will be slow and bad. Conversely, if we are expected to be fast and excellent, we will rise higher than otherwise to meet those expectations. A few more minutes at first seems reasonable, but I would be doing my practice essays according to a stricter time limit. If you calculate out the examination requirements, you should be writing 1200-1600 words per hour give or take: this means ideally 200-300 words per paragraph, with four bodies for stronger students and three for slightly less so (or people who expand more than usual in their paragraphs). Language analysis and context obviously tweak these paragraph rules, and very fast students will write more than this.
So, if you want to practise doing essays with longer time limits in preparation for SACs that have them, I would concentrate on formulating an additional paragraph or two rather than waffling in the paragraphs you already have.
In the meantime, I just made some amazing chocolate peanut butter frosting and overloaded a cupcake to "use it up". I think I'm going into a sugar coma.