I haven't used WEM paints, but I know they are supposed to be good, Muller uses them so he is probably the best person to advise. However, an average enamel model paint should not take ages to dry; are you certain they have been stirred fully, in order to mix the pigment with the carrier? If they have been sitting on a shelf for some time, in the shop, warehouse or your modelling bench, they will have settled, and they may need a lot of stirring, more so satin than matt paints, and, some colours have a slightly heavier pigment, needing even more stirring. BTW, even satin finishes would benefit from a gloss coat to help with decal application, to ensure they 'bed down' smoothly, without silvering.