Because both Z wave and zigbee are mesh topologies, Messages can bounce around the network for a little bit, which means you can’t guarantee forced sequencing. For this reason, the official SmartThings features will not let you schedule things closer together than one minute.
There is a community-created rules engine, CORE, which will let you put in a shorter time period, but they can’t guarantee that it will work. The fewer devices you have, the more likely it is to work, so people do use it.