To counter act not accounting for DST, determining the first weekend and april and last weekend in october will allow a user to adjust for this.
Well it would do, so long as you're in a place that uses those dates. But it would still be wrong in the EU, for example, where the clocks go back on the last weekend of March, not the first one in April.
And presumably it'd be even more wrong in the southern hemisphere, where I'm guessing the clocks change in the opposite direction?
Now you could do lots of research and then allow for all these things, or ...