I will try.

The workbook is calculating workinghoures for the employees and give a visible look at the covering of needed employees.
The cells we are working on here is for 1 employee (me).
U1!D4 and U1!E4 is in the format [t]:mm
U1!F4 is standardformat
Target cell is standardformat

I have made a little change (non destructive ) in the formula so it looks like this:
 =HVIS(ELLER(ER.TOM(Uge1!D4);(ER.TOM(Uge1!E4)));"";_
HVIS(MINUT(Uge1!D4)>0;TIME(Uge1!D4)&"."&MINUT(Uge1!D4);TIME(Uge1!D4))&"-"&HVIS(MINUT(Uge1!E4)>0;TIME(Uge1!E4)&"."&MINUT(Uge1!E4);TIME(Uge1!E4))_
&HVIS(ER.TOM(Uge1!F4);"";HVIS(ELLER(ER.TOM(Uge1!D4);(ER.TOM(Uge1!E4)));Uge1!F4;" /"&Uge1!F4)))
Here is the list (RP! = Rulleplan!:

Uge1!D4=Empty | Uge1!E4=Empty | Uge1!F4=RP!D4 | Target cell = Empty
Uge1!D4=Empty | Uge1!E4=Empty | Uge1!F4<>RP!D4 | Target cell = Uge1!F4
Uge1!D4=Filled | Uge1!E4=Empty | Uge1!F4=RP!D4 | Target cell = Empty
Uge1!D4=Filled | Uge1!E4=Empty | Uge1!F4<>RP!D4 | Target cell = Uge1!F4
Uge1!D4=Empty | Uge1!E4=Filled | Uge1!F4=RP!D4 | Target cell = Empty
Uge1!D4=Empty | Uge1!E4=Filled | Uge1!F4<>RP!D4 | Target cell = Uge1!F4
Uge1!D4=Filled | Uge1!E4=Filled | Uge1!F4=RP!D4 | Target cell = Uge1!D4&-&Uge1!E4
Uge1!D4=Filled | Uge1!E4=Filled | Uge1!F4<>RP!D4 | Target cell = Uge1!D4&-&Uge1!E4& /&Uge1!F4

Example:

Rulleplan!D4=700

Uge1!D4 [Empty] | Uge1!E4 [Empty] | Uge1!F4 [700] | Target Cell [Empty]
Uge1!D4 [Empty] | Uge1!E4 [Empty] | Uge1!F4 [900] | Target Cell [900]
Uge1!D4 [7:00] | Uge1!E4 [Empty] | Uge1!F4 [700] | Target Cell [Empty]
Uge1!D4 [7:00] | Uge1!E4 [Empty] | Uge1!F4 [900] | Target Cell [900]
Uge1!D4 [Empty] | Uge1!E4 [15:00] | Uge1!F4 [700] | Target Cell [Empty]
Uge1!D4 [Empty] | Uge1!E4 [15:00] | Uge1!F4 [900] | Target Cell [900]
Uge1!D4 [7:00] | Uge1!E4 [15:00] | Uge1!F4 [Empty] | Target Cell [7-15]
Uge1!D4 [7:00] | Uge1!E4 [14:30] | Uge1!F4 [Empty] | Target Cell [7-14.30]
Uge1!D4 [7:00] | Uge1!E4 [15:00] | Uge1!F4 [700] | Target Cell [7-15 /700]
Uge1!D4 [7:00] | Uge1!E4 [14:30] | Uge1!F4 [900] | Target Cell [7-14.30 /900]


The part of the formula that makes the U1!F4-part of the targetcell look different
("900" or "7-14.30" or "7-14.30 /900") is this:
&HVIS(ER.TOM(Uge1!F4);"";HVIS(ELLER(ER.TOM(Uge1!D4);(ER.TOM(Uge1!E4)));Uge1 !F4;" /"&Uge1!F4)))

Tried to make the listings look like tables. Not easy in here