That’s right. So your desire outstrips your means to achieve it. You can learn something new. Javascript rules will have most in common with Blockly.
In OH3 it is one at a time, further triggers will be queued.
But don’t worry about that, when using timers properly a rule starts a timer with an independent existence, and then the rule will exit, ready to run again.
Next time, depending on conditions, it might cancel or reschedule the independent timer.
It’s a very common technique e.g. for door lights timers, and the current lack of it is a major Blockly handicap that is being worked on.
An alternative approach is to use a dummy Item with ‘expire’ feature scheduling. This is so basic that it is difficult to cancel or reschedule, but it can be done. A second rule can then trigger off the expring dummy Item to perform whatever action is needed.
EDIT - that reminded me to produce this