Hi and welcome to the 'club'
Theres a lot of variables involved in the heating of the water, such as what temperature the 'cold' water is, what temperature your 'target' is, what power of heater you have combined with how much water.
All I can offer you at this time is that in my 300L tank I have a 300W heater, (so 1W / L), and that take about 12 hours to raise the water from around 7 degrees C to the low 20s, and then up to 30 degrees within around 24 hours. Also this tank is in my living room, so it's a central heated room. If the tank was in a cold ambient space it would take longer I am sure).
As a note on the 30 degrees... the tank wouldn't normally be this warm but I am currently doing my fishless cycle on it, so the temperature is elevated for that. If you are a new starter and don't know about fishless cycling I would strongly suggest you take a read of the following thread:
Fishless Cycling