Copying what Daniel did, just ready for export.
axis = {1, 1, 1}; l = {-7, 7}; s = Table[ Plot3D[2*z[x, y], {x, -5, 5}, {y, -5, 5}, PlotRange -> {l, l, l}] /. gg : GraphicsComplex[___] :> Rotate[gg, theta, axis], {theta, 0., 2. Pi}]; Export["c:\\test.gif", s]

The following options are available for exporting gifs (according to the docs):
"AnimationRepetitions" how many times the animation is played before stopping "Background" background color shown in transparent image regions "BitDepth" bits used to represent each color channel in the file "ColorMap" color reduction palette, given as a list of color values "GlobalColorMap" default color palette for individual animation frames "DisplayDurations" display durations of animation frames, given in seconds "ImageCount" number of frames in an animated GIF "ImageSize" overall image size "RawData" array of color map indices "Comments" user comments stored in the file
I have used "DisplayDurations" in the past and it worked.
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