I don't normally put leeks in until after first early spuds come out, around June time. Leeks are normally in the through winter, so no rush to plant out.
Good time then, Heygrow, the soil has been mucked around with, is nice and opened up, easy to dibble and the process of planting late leeks then makes the most of the ground!
I made the mistake of planting some earlies one year, and they mostly failed, looking miserable by the time we normally require them, from November onwards! (Then I joined this Allotment site and started to know better..;0)
...still learning...