Start by opening a sky image.
Create a rectangular selection using rectangular marquee tool towards the left edge.
Press Ctrl+J to duplicate the selection in a new layer. Move it to the right edge of the image.
Press Ctrl+T. Right click the layer and select flip horizontal.
Merge both the clouds layer. Select stamp tool (s) and start cloning the area of the joint.
Create a duplicate of the sky layer. Move the original layer towards the left and a duplicate towards right.
Merge both the layers. these steps are essential for creating a seamless loop of the sky animation.
Insert a clock image in the main file.
Change the layer mode to linear burn.
Knock out the hard edges using eraser tool with a soft brush settings.
Create a selection of the clock hand.
Press Ctrl+Shift+J to cut and paste the selection in a new layer.
Clone to fill the cutout and the second hand.
Unhide the previously hidden clock hand layer.
Create a duplicate of the hand layer. Press Ctrl+T. Move the anchor point to the center of the hand.
Rotate the hand 60°.
Create 4 more duplicates of the hand layer and keep rotating at the 60° increments.
Open animation window. For the first frame hide all hand layers.
Duplicate frame. Move the clouds layer towards the left. Take care to move as much as to achieve the initial position of the clouds after movement.
Click tween button in animation window. Apply settings as shown.
Select and remove the last frame in animation window.
Select the first frame. Unhide the original hand layer.
Select the second frame. Hide the original hand layer and unhide the second duplicate of the hand layer.
Similarly keep selecting successive frames and hiding/unhiding clock hand layers.
Press Ctrl+Alt+Shift+S to save an optimized animated GIF.