The storage heaters that iO Energy sells take 7-8 hours to fully charge from 0% to 100% capacity. They may not, however, need a full charge each day. So the exact answer depends on whether your heater already has some charge or not.
The storage heaters that iO Energy sells can also be programmed to charge during two different time windows every 24 hours. This allows the system to be inexpensively charged by taking advantage of off-peak electricity pricing from the grid and/or solar power from your rooftop.
The largest storage heater that we sell can hold a massive 32 kWh of energy and heat a 90 square meter room. On iO Energy's residential rates it will cost approximately $3 to fully charge, compared to a bit over $4 for an equivalent amount of energy from natural gas heating.