vonmasti lujvo

x1 is April/the fourth month of year x2 in calendar x3.

Duration. For date, use masnvo. Cf. pavmasti, nanca.

In notes:

lanma'i
x1 is April of year x2 in calendar x3.
pavmasti
x1 is January/the first month of year x2 in calendar x3.
vonmast
April.