If "Uge1!F4<>Rulleplan!D4" is true the formula now shows only Uge1!F4 even if data is entered in both Uge1!D4 and Uge1!E4.

If i use:
=HVIS(OG(Uge1!F4=Rulleplan!D4;OG(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))&" "&Uge1!F4)
and both Uge1!D4 and Uge1!E4 is blank the formula shows "0-0 700", where the zeroes an the - comes from Uge1!D4 and Uge1!E4.

Maybe the rest of the formula should be changed. The first part seemes to do what it is supposed to do.

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))&" "&Uge1!F4)