The generated code for a stateflow chart which has one of the conditions for state transitions as either 'after(n,tick)' or 'after(n,sec)' indicates that in both the cases a counter is implemented to keep track of time. The only thing changes is the condition which depends on how 'sec' and 'tick' are interpretted. The following example illustrates this idea:
Consider the following stateflow chart:
The generated code for this looks as follows:
If the condition in stateflow chart is changed to 'after(n,tick)' format, the generated code looks as follows:
In both the cases, the stepsize is considered to be 0.2 sec. The conditions in the first case considers how many steps of size 0.2 sec are required to complete 1 sec and 2 sec respectively to make a state transition whereas in second case it considers just the number of steps mentioned in the condition itself (that's how 'ticks' are interpretted).
For more information on 'after' command you can have a look at this documentation page.
Hope this helps!