I have found the shelf life to be around six months. After that it starts to break down and form globs of paint which is very hard to mix or thin. Someone told me that if you shake it up every two to three months it will make them last longer. In two days time the paint should be good as long as it is covered.
Berny
Phormer Phantom Phixer 
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.