Timer switch is not as good as Light detector Sensor Switch (Photo sensor). It will automatically switch from Wapda to your Solar Set up when there is visible light of Sun in the horizon in the morning, so that your Solar panel takes over automatically. its also cheap only $5 (Rs. 500). Here is the link on Ali Express.
Keep in mind you will need a relay switch to turn off the Wapda power as well. You can make some sort of brilliant set up yourself, using relays and solar photo cells to make a switch that turns off the Wapda Main supply with a relay switch. Or you can use timer to turn it off. Talk to some electrician in your neighborhood.
This light photo censor will help in turning on the Solar Set Up, as this is a switch that turns a solar set up on, when Sun is up and Turn any electrical setup off, when Sun if down, automatically.
http://www.aliexpress.com/item/AC-DC-220V-Dusk-till-Dawn-Auto-Street-Lamp-waterproof-light-Sensor-Detector-switch-Automatic-Photocell/32239108599.html