Hi,
just make an variable (in the cannon instant) called "shoots" and a booleon called "reload"
On every shoot check if "shoots is >0.
Than subtract 1 from shoots.
If shoots =0 set reload to true.
if reload is true (and a trigger ones) wait 2 seconds then set "shoots =5" and reload to "false"
thats ist.
maybe you should also make a timer for you can only shoot every 1 second or something like that.