If you do not have the event onset (or duration?) times, then you are missing a serious part of the experimental data!!
There are ways to guess the times, but those are not likely to be successful unless you have a block design (long duration events) activation cycles visible in major areas such as visual and/or motor cortex.
You could do an ICA type of analysis, which is very different than GLM. However, we don't have much ICA analysis stuff in AFNI.