ESP gives you indication as what the timing looks like early in the flow. In magma flow, once you are done with the " fix time $m $l "it will print a gain report table ; the number of cells with gain less than 1 should be very less ; typically 1% and if it is more , you might have a timing convergence problem and so depending on your timing violations, you need to go back and fix it..this is just a recommendation ..