ity uktva yajñiye kale
vavre yuktan sa rtvijah
Sukadeva Gosvami said: Having said this, King Yudhisthira waited until the proper time for the sacrifice was at hand. Then with Lord Krsna’s permission he selected suitable priests, all expert authorities on the Vedas, to execute the sacrifice.
The great Bhagavatam commentator Sridhara Svami explains that the proper time for the sacrifice mentioned here was the spring.