Hot Water Cylinder heating?

I am just looking for some advice. I currently use a lot of hot water in house. I have the below cylinder installed. Put in brand new last year to try and stop heat loss

https://www.goodwins.ie/products/insulated-copper-cylinder-indirect-1050x450mm-42x18-2310525.html?filter_set[]=9,49

I put timer in which runs in middle of night on cheaper electricity. In morning the tank should be full.

By the time kids have bath at 6 the water was not hot mostly because it was used up so I had the timer kicking in from 3-6. This was done via immersion.

Im trying to reduce the electric costs so was talking to friend and he said to just use boiler in winter months as it is going at same time. So I switched on this evening to heat water. I have a dual system. The main questions are:
How long would it take to heat 150ltr using the boiler? just an average, I know it wil be different.
If using the immersion how long should it take to heat a full tank?

Thanks for advice