The commands to achieve this are :
Extend by Grid
Shorten by Grid
which as the name suggests, shortens/extends the selected event length by the grid quantization length.
BTW, there are also similar commands for midi notes :
Extend Notes by Grid
Shorten Notes by Grid
Though I am not sure if these commands are natively present in S1 or are included in Navigation Essentials script.
https://s1toolbox.com/navigationessentials