New Post: How to set tEXT chunk in PNG files?

Do you want to set the tIME chunk or do you just want to read it? There could be a couple of reasons why Magick.NET is slower then the .NET encoder. Magick.NET will always decode the pixels of an image I am not sure if the .NET encoder also does this. And as you noticed the compression is much better. You can control this with the -quality property of the image. Using another value might be quicker. I found the following detailed explanation in the code:

Untangle the "-quality" setting:

Undefined is 0; the default is used.
Default is 75

10's digit:

   0 or omitted: Use Z_HUFFMAN_ONLY strategy with the
      zlib default compression level

   1-9: the zlib compression level

1's digit:

   0-4: the PNG filter method

   5:   libpng adaptive filtering if compression level > 5
         libpng filter type "none" if compression level <= 5
            or if image is grayscale or palette

   6:   libpng adaptive filtering

   7:   "LOCO" filtering (intrapixel differing) if writing
         a MNG, otherwise "none".  Did not work in IM-6.7.0-9
         and earlier because of a missing "else".

   8:   Z_RLE strategy (or Z_HUFFMAN_ONLY if quality < 10), adaptive
         filtering. Unused prior to IM-6.7.0-10, was same as 6

   9:   Z_RLE strategy (or Z_HUFFMAN_ONLY if quality < 10), no PNG filters
         Unused prior to IM-6.7.0-10, was same as 6

Note that using the -quality option, not all combinations of
PNG filter type, zlib compression level, and zlib compression
strategy are possible.  This will be addressed soon in a
release that accomodates "-define png:compression-strategy", etc.