Hi @alexlrca ,
Could you please share a bit more about your issue?
Do you mean that the GIF freezes when the Timer control hits the end (1 second)? Do you mean that the LoadingScreen could not navigate to your Screen2?
Based on the issue that you mentioned, I have made a test on my side, and don't have the issue that you mentioned. Please set the Duration property of the Timer control to following:
3000
Set the AutoStart property to following:
true
Set the OnTimerEnd property of the Timer control to following:
Navigate(Screen2)
Note: Please make sure you do not specify any formula within the OnTimerStart property of the Timer control.
Actually, I think it is not necessary to add a LoadingScreen to achieve your needs. I think the LoadingSpinner property of the screen could also achieve your needs:

Please check and see if the following video resource could help in your scenario:
https://www.youtube.com/watch?v=YfYf-AkY1P8&feature=youtu.be
Best regards,