Can app receive immediately handler from FCM?

I would like to transmit the data received from UART using FCM service by UDP.
The application on module must judge “the termination of data received from UART” with a data interval, and data interval must be within 100ms.
But, there is about 1 second between the first FCM data handler call and next FCM data handler call, if the data is sent to the module by the UART with 1200bps.
So, app judge incorrectly the termination of data.
(FCM service is buffering data?)

Is there a way for an application to receive handler immediately from FCM service when module receive data from UART?