Let's say a program perscribes 3 sets of dealifts with 90 second rest between set followed by 3 sets of pull-ups with 90 seconds rest. Does this mean that the rest period between the last set of deads and the first set of pull-ups should also be 90 seconds? Or should this rest period be longer/shorter depending on how you feel?
I would go with 90 seconds if the exercises are for different musclegroups. Perhaps a bit longer if they are for the same muscle group.
Also, take into account the time it takes to put the weights away from your previous exercise and prepare for the next. This usually exceeds the rest period anyway.
Because I gym at home and don't have ALL the equipment I would like I often substitute certain exercises, so the time I spend unracking & racking up for the next set usually covers most of my rest period.
But yes, in that example a 90 sec rest is about right between different exercises.