you can use waver
I did this recently
waver -dt 2.5 -EXPR 'step(t+0.01)*step(2.51-t)' -numout 200 \
-tstim `1dtranspose stim_times.1D`
replace 2.5 and 2.51 with your actual TR and TR+0.01 (arbitrarily chosen small value). Replace 200 with the number of time points in your dataset.
