The snapshot’s name is used by (TrueNAS’s) zettarepl. Rather than use metadata (slower), it parses through the snapshot names (faster). That’s why it’s important to include the date and time information in the name itself.
Yes you can, and there is no limitation from vanilla OpenZFS (except for certain characters). But with TrueNAS, there’s a reason why a standardized (date-time) naming convention is used. (See above.)