I would tell the parents that the time it takes for them to comfort him at drop off is the amount of time it's going to take for him to quit crying once they leave. So if they do ten minutes of cuddles you will get about ten minutes of cry time when he has to balance out the extra he got that he didn't need.

Once the parents leave I would just have him sit and say "you cry". Don't put any emotions to it... just acknowledge that "you cry". Let him know it's all good and that you aren't going to do anything but let him express his little feelings. He has a right to express himself and he can sit right there and have at it.

When he's done you say "nice job. go play toys".