commitment to lock time t (can be spent once real_time >= t)

C(x, t) = xG + tH

new commitment to same thing
C(y, t) = yG + tH

sign in a ring commitment to zero
C(x, t) - C(y, t) = (x - y)G

then calculate, where t’ is a block time in which the tx is spendable (or any later block)
P = t’H - C(y,t)

then do a range proof on P, since if t’ - t is negative then it will roll over