Clairol root touch up- stubborn greys

[checkmateboom]

I know the packet says 10 mins but I'm pretty sure that won't touch the sides on my crazy stubborn greys, anyone with similar problem had success with leaving it on longer?

I leave it the full 15 for "stubborn" greys... If works well for me, except for around my temples which always reappear grey in a week or so...
I wonder if shampooing straight after use is having an adverse effect? The instructions on these sorts of things usually say rinse, then use that (hideous) conditioner. They don't tell you to shampoo.But my hair needs washing every day - and I like to shampoo to ensure all the dye is removed. Could this reduce the effectiveness of the dye?

Have you thought about just using your regular hair dye? I just mix up an equal portion of colour to activator every fortnight, using a dye brush in a mug. Then apply to my roots and leave for 45 min. Each box then lasts about 4 uses and I don't have to buy touch up dye.