Cam duration question

My Dart restoration is coming along great. Getting ready to do some assembly finally. Now I bought this car way back in 2003. We are going through the 440. We are pulling the cam and going to install new cam and lifters.
The cam coming out is the
B/RB 361-440, 284/484 Hyd Flat Tappet

.484" / .484" Lift. 241/241 Duration @ .050" 108 + 0 L/C

One Bolt Pattern

Street / Strip

The one I can get from Mancini racing is
B/RB 361-440, 284/484 Hyd Flat Tappet

.484" / .484" Lift. 239/239 Duration @ .050" 108 + 0 L/C

One Bolt Pattern

Street / Strip

Is there a big difference in the duration going from 241 down to 239?