Google Sheets WENN Date and Checkbox

i'm trying to figure out, how I can get my formula working. It's telling me I need a valid date.

So if i'm going for this :

J3=checkbox, D5=date formated with =today(), G5=number between 1-30

=WENN(J3=FALSE;D5+G5) This works fine ( today() + 1-30 )

Now here comes the error :

=WENN(J3=FALSE;D5+G5;);WENN(J3=TRUE;D5+7;) This does not work because now it's telling me I need the valid date.

So my question is, how I can get it work?