z= b0+b1*X+b2*Y-b3*X*Y

Y (time) and X are continues variables

If I am not mistaken, we cannot interpret an isolated main effect, when there is a significant interaction; however, we can conditionally interpret in a whole model . If we check the effect of X on z when the time is different than 0 and and equals to zero, the equations then becomes as follow,

z1= b0+b1*X+b2*Time-b3*X*Time

z1=b0+b1*X+b2-b3*X -> y1=b0+(b1-b3*Time)*X+b2*Time

The effect of X, while increasing by one unit, on z1 is b1-b3*Time. So as time increases the effect is moving to more negative side.

z2= b0+b1*X+b2*Time(0)-b3*X*Time (0)

z2=b0-b1*X

The effect of X, while increasing by one unit, on z2 is

**positive b1**and it actually increase the z2. What does this practically mean? Or, should we conclude that as the Time increases the effect of X on Z1 is decreasing

**b1-b3*Time**and you cannot individually check each time point but treat it as continues ?

Last question, is it important if main effects here X and Time are significant or not if interaction is significant.

Can someone please help me to understand this kind of equation?