I don't work in imperial measurement so not sure what your measurements are in relation to millimeters but if your wear indicators are approaching the tread then its time to change. If you look into the tread, you should see small blocks inside the tread which are your wear indicators.

Once they are level then your tyres are done and due a change. Here in the UK we have a legal limit for tread depth which is 1.6mm. I prefer to change when the tread depth is less than 2mm as the risk of aquaplanning increases with reduced tread depth and the UK has a lot of rain.