Why does Cydia say pending tss queue / request on my iPhone?

No worries, it could take days or weeks for the firmware SHSH blobs you've saved to appear in Cydia. As long as you have properly saved your SHSH blobs using TinyUmbrella you are covered for a firmware downgrade. TinyUmbrella saves your SHSH blobs locally on your computer hard drive as well.

The delay is due to intermittent Cydia updates by the developer Saurik. Once Cydia is updated internally the latest saved SHSH blobs will appear in the Cydia app on your jailbroken iPhone. In the meantime, as long as TinyUmbrella has saved your SHSH blobs locally you can ignore the tss queue message.