Nested IF function to count days from milestone dates

I have a spreadsheet (attached) that give me 5 dates of certain company milestones, I need to code the report so that I can count the days between each milestone for instance:

If G2 and H2 are blank, return a zero in C2
If G2 has a date but H2 is blank, return Todays date – G2 in C2
If G2 and H2 both have a date, return H2-G2 in C2

I was trying something like this but cant figure it out [=IF(AND(ISBLANK(G4),ISBLANK(H4)),0,IF(AND(ISBLANK(H4),ISBLANK(G4)=FALSE),TODAY()-G4, H5-G4)]

Thanks for any advice!

Glen