Could you read the information for different types of SU8 data sheets regarding the references of processing conditions in the website of http://www.microchem.com
If you've exposed, developed and hardbaked it then it will remain structurally and chemically sound pretty much indefinitely. You may find this to be the most useful website in the world: http://memscyclopedia.org/su8.html, much more trustworthy than the datasheet.