What exactly did Rodney do for 25 years?

[jdbond]

A whole new Math to do what though? Calculate the type of solar flare needed? Something we've seen carter do in a space of 5 minutes? I don't buy it.

To ensure that what happened by "accident" will be repeated by precise calculation. Solar flares cause time travel but they don't guarantee that you will return exactly where you begin.

[Athgar]

Coding isn't the sort fo thing that requires a new math though.

All modern programming languages are based around lambda-calculus. The currently held theories of computability state there are infinitely many calculations that are not possible. If McKay wanted to do such calculations and had managed to work out how to do it he would certainly need a new system of mathematics before he could get a computer to actually crunch the numbers. I'm not sure the writers were really thinking along these lines but it is logically plausible

And the solar flare thing, thats not how it works. The calculations don't get more complex jsut becasue it's a larger distance, thats not how time works.

The calculations don't get more complex per se but you have to be much more accurate over a longer period because minor errors produce an increasingly inaccurate result. In particular it is worth considering that a number of mathematical problems have solutions that take an extremely long time to return a result (e.g. the travelling salesman) and usually heuristic algorithms are used which are inherently inaccurate.

To me it's plausible but I happily admit I'm not the most nitpicking viewer