If janazah is ready in the makrooh time then the janazah salah can be prayed the same time, rather it is better to pray it. But, if the janazah was ready before makrooh time and meanwhile makrooh time started then it should be delayed a bit more so that the makrooh time passes. In this situation, it is makrooh-e-tahreemi to offer janazah salah in makrooh time.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband