Eric - 02.10.2018
I just looked at:

http://www.gas-tankstellen.de/menu.php

LPG price was €0,609 per litre on the 11th of July 2018.

Opening hours are listed as Monday till Sunday from 7 till 20h. I have not been there myself, so I only cite what I found on this other website. Gas-Tankstellen is often less updated, because you have to sign in.

From my 20 years of experience, it could be interesting to compare the price at Grenz Gas in Gewerbestraße in Süderlügum, because gas stations on main roads are often more expensive than gas stations who are hidden at the back of some industrial zone. Take into consideration that the mixture of propane and butane could be different, which makes it hard to compare prices in a fair way.

Süderlügum is your place to fill up with LPG if you travel north. Please do check if your car is still running on unleaded fuel, before you cross the Danish border; In Denmark, LPG costs more than unleaded petrol!

Eric - 02.10.2018
Please excuse me, this is the correct and hassle-free weblink:

http://www.gas-tankstellen.de/menu.php?jump=detail&tanke=14869

It looks as if Hem is now called Elan - The address remains the same -

And it says 'pay by card' please