How long can a President Be away from duty on grounds of ill-health?

Dateline, January 19, 2017: President Muhammadu Buhari left the shores of Nigeria for medical vacation in the UK.

It’s been 27 days since he traveled.

His absence left a vacuum which was filled with a formal transfer of power to Vice President Yemi Osinbajo.

There are worries, however, that the Nigerian constitution does not provide adequately for the length of time an ailing President or Governor would be bed-ridden before his office is formally declared vacant.

The dilemma created by this gap is that if not dealt with, the acting President or Governor would be exercising ‘double powers’ not envisaged by the constitution.
Is it not about time that National Assembly gave due attention to the perceived legal vacuum?