I don't know what laws are like in Germany, but in the US, it's easy enough to get divorced. It's just very expensive. Putting an expiration date on a marriage will not have any effect. If anything, it will encourage more women to get pregnant in order to keep their husbands on beyond the deadline.
A far more practical reform would be in divorce law. Right now, in the US, we have what are called "no fault" divorces. This means that regardless of who was responsible for the dissolution of the marriage, the divorce is granted with the assets of the marriage divided in half between husband and wife. Regardless of who contributed what to the marital wealth, it's still distributed 50/50. Also, there is a persistent lean in favor of the wife in the courts, as she is usually entitled to alimony, as well as preferential child custody. Despite "equality", women are treated as if they are delicate and must be protected, sometimes from themselves. No fault divorce was originally a reform measure to remove the legal fiction of cause, which had to be fabricated in some instances where the couple simply didn't want to be married with no specific reason. However, it's gradually become a tool of abuse. This is why prenuptial agreements have become so popular in the US.
A useful measure of reform would be to remove the 50/50 split entirely, and divide the assets based on actual income. If the husband earns 100,000 and the wife 50,000, then it would be a 2:1 split. Also, parties would earn points for marital infractions, such as infidelity, physical abuse, sexual avoidance, etc. The more infractions, the more the favor to the other spouse. Short of committing an outright felony, there is no legal protection for spouses mistreated in such cases.
