Is it permissible to delay the first obligatory Umrah until Ramadan—while being able to perform it at the beginning of Shaban—due to its superiority in Ramadan?

The scholars have agreed upon the permissibility and virtue of 'Umrah, but they differed on its obligation, holding two views: one is that it is Sunnah (recommended) (Abu Hanifa and Malik), and the other is that it is obligatory (Al-Shafi'i and Ahmad). The preponderant opinion is that it is obligatory.

If the conditions of obligation are met (financial and physical ability), it is best to perform 'Umrah immediately, based on the statements of Al-Hajjawi and Ibn 'Uthaymeen, and relying on Allah's saying: "And [due] to Allah from the people is a pilgrimage to the House" and "So race to [all that is] good." This is also because the default rule for a command is that it implies immediacy, and because a person does not know what might happen to them.

Nevertheless, if the delay is for a short period (like a month) and there is a benefit in it (such as performing it in Ramadan), there is no harm in that, especially since some scholars have stated that 'Umrah is recommended, and the Shafi'is view it as being on delay, not immediate, which allows for its postponement to a virtuous time if the time is near and one is reasonably certain that the ability will remain.