According to output, my within-subjects time effect is not significant, timexgroup effect is significant, between subjects group effect is not significant.
This means that over groups, there is no effect of time, and over time, there is no effect of groups.
However, the effect of time does differ between groups.
Imagine that " temperature" is time here, and the lines represent 2 groups:
There is no main effect of time (i.e., the mean of the 2 groups is the same at T1 and T2).
There is no main effect of group (i.e., the average between T1 and T2 for Red is the same as for Blue).
THere is an interaction (i.e., the effect of time on the outcome is different for Red than for Blue, as Red decreases and Blue increases).