Hey pretty basic question, but the warning light for low brake pads came on tonight, my week ahead is pretty full how soon does one need to change these after the light comes on, or how do I check them myself to see?

Cheers!

 

The warning is meant to trigger when there is 4 mm thickness left on the pad, so even if it triggers a bit late (say 3 mm) you have plenty of meat left on them yet, no need to panic.
That said, you don't know which sensor triggered (front or rear), and it's possible that one or more of the unsensored pads is worn a lot more. There are two sensors, LHS front and RHS rear, and both on the inner pad, so that's only two out of eight pads being monitored.
So I recommend you whip the wheels off and have a look, it's not that hard.
The outer pads are fairly easy to check, you can poke your head inside the wheel well and look at them side-on, but the inner pads are a little harder to see with taking the calipers off, you need to make like a snake under the car with a good torch and maybe a mirror.