In reply to samir singh:
$timeformat affects how the %t is printed in $display. So you specify $timeformat only once as shown above in an initial block, then any $display having %t will function as you described. By default %t will print time w.r.t. the smallest precision in the simulation cluster with no time units. However you can change the default as above. If you added the above $timeformat code in your example above, your $display will print time as “7.00 ns” instead of “70000”. Does this answer your question?