Programming hot water on twice per day, or leaving it on all time 24 hours, makes little difference on energy saving.
A modern unvented hot water cylinder (white hot water storage tank normally in upstairs airing cupboard) is very energy efficient. That means, it has very little heat loss while storing hot water. It is also not as warm as before in the airing cupboard compared with an old type of vented hot water cylinder.
When hot water temperature reaches 60C to 65C degree inside the cylinder, the boiler stops heating hot water, no gas is wasted even hot water is still on at the programmer.
Total amount of energy being used for hot water is mainly determined by how much hot water your family has consumed, not by the on and off time.