Am I limited in the amount of days/months I have to serve him? Are there obvious legal advantages that would motivate him to delay being served?
Family Law Attorney
If your process server can't get your husband served after diligent efforts, he can sub-serve your husband by serving the papers to somebody at your husband's home or work over the age of 18 years and mailing a copy of the papers to your husband. You do have limited time to serve your husband, so he should be served as soon as reasonably possible.
Please note that this answer does not constitute legal advice, and should not be relied on, as each situation is fact specific, and it is not possible to evaluate a legal problem without a comprehensive consultation and review of all the facts and court pleadings filed in the case. This answer does not create an attorney-client relationship.
Divorce / Separation Lawyer
Be careful. Your husband might be trying to establish residency elsewhere or is simply shopping for an attorney before being served and wants the attorney to have the full 30 days in which to respond. More likely is that he does not want the divorce and is hoping that a delay will cause you to change your mind.