Group and compare data

I have som XML that looks like this:

<Forhandler>
        <Forhandler>
                <navn>Dealer name</navn>
                <email>mail(_at_)adress(_dot_)dk</email>
                <adresse>road 11</adresse>
                <postnr>9999</postnr>
                <by>city</by>
                <telefon>4444444</telefon>
                <aabningstiderMan>7:30 - 17:30</aabningstiderMan>
                <aabningstiderTirs>7:30 - 17: 30</aabningstiderTirs>
                <aabningstiderOns>7:30 - 17:30</aabningstiderOns>
                <aabningstiderTors>7:30 - 17:30</aabningstiderTors>
                <aabningstiderFre>7:30 - 17:30</aabningstiderFre>
                <aabningstiderLoer>10:00 - 14:00</aabningstiderLoer>
                <aabningstiderSoen>Efter aftale</aabningstiderSoen>
        </Forhandler>
        <Forhandler>
                <navn>Another dealer</navn>
                <email>another(_at_)adress(_dot_)dk</email>
                <adresse>another road</adresse>
                <postnr>5555</postnr>
                <by>big city</by>
                <telefon>5555555</telefon>
                <aabningstiderMan>07.30 - 17.30</aabningstiderMan>
                <aabningstiderTirs>07.30 - 17.30</aabningstiderTirs>
                <aabningstiderOns>07.30 - 17.30</aabningstiderOns>
                <aabningstiderTors>07.30 - 17.30</aabningstiderTors>
                <aabningstiderFre>07.30 - 16.00</aabningstiderFre>
                <aabningstiderLoer>Lukket</aabningstiderLoer>
                <aabningstiderSoen>Lukket</aabningstiderSoen>
        </Forhandler>
</Forhandler>

What I am trying to accomplish is to group the opening hours so they
look more nice.

For the first dealer the result would be:
Mon-Fre 7:30-17:30
Loer 10:00 - 14:00
Soen Efter aftale

For the second dealer the result would be:
Man-Tor 07.30 - 17.30
Fre 07.30 - 16.00
Loer-Soen Lukket

I have tried som xsl-choose loop, but I went sour in the complexity of
variations, what if a dealer have diffent opening hours every day of
the week.

So I thought, there must be at better approach on how to achieve this.
Is the use of keys a better approach, and if so, how?

/Thomas