You can program this into your GAMS program. The GAMS/CPLEX-link returns with a license error in the solver status. If this happens, you could put your model to sleep for x seconds and try again:

repeat
  solve mymodel min z using mip;
  if (mymodel.solvestat=7, display$sleep(5) 'sleep 5 seconds for Cplex
license');
until mymodel.solvestat<>7;

If your version of GAMS does not have the sleep command, you could call 'execute “sleep 5”;' to call an external program.