We recently had a similar discussion in PI SDK Development forum: Event pipe polling interval under 1000 ms ?
It turned out that PI SDK is rounding to the next full second and I can imagine it's similar with AF SDK. We have however contacted development for an answer to your question.
Why do you need updates faster than each 100 ms?
PIDataPipe in AF SDK queries the PI Server when you ask. There is no delay, thus there is no limit.
PI SDK sets up an independent polling loop for its EventPipe (5 seconds by default). The PI SDK will copy items out of the server into a client side queue in a separate thread. The query from your program to the PI SDK is just pulling items out of this client side queue and not going back to the PI Server to look for newer events. In AF SDK, there is no client side queue.