Hey there,
For blonde i'd suggest going to a professional. When darkening eye brows you have complete control over the colour, basically the longer you leave it on the darker it gets. It only takes a VERY short ammount of time to tint brows (sometimes under 1 minute depending on the products used)

When lightening, the hair has to go through different colour shades to achieve the 'blonde' look, rather than red, orange, yellow, copper etc and its the bleach that controls it. If you take it off too early you end up with a range of funky colours that could be the end result. If you put more bleach on it could react quicker the second time and you don't know what you end up with!

Best to stick with a professional
Good luck