Jitter/gap issue with collected mixed design data

Hi all,

I have data from a mixed event/block design in which faces are presented for a fixed 1000ms and responses are given for a fixed 3000ms in blocks of 20 seconds (5 trials) after which a physiological condition changes and the face/response paradigm repeats for another 5 trials/block (64 blocks).

The issue is that there is neither a jitter between face/response trials, nor is there a gap between condition changes after each 20s block. The trials appear immediately after one another and the blocks change instantaneously with neither having gaps for the hemodynamic response to settle.

What issues will I have with data from this design and are there any ways to combat this flaw in the data?

I am using fsl at present.

Thanks for any advice in advance!