Don't worry. Nerines are autumn-flowering bulbs so you don't need to plant them at the same time as spring-flowering bulbs. Planting in the spring will be fine. Have a look at our plant feature on Nerines at:
Good luck with your nerines. I think they are fabulous flowers. I do not seem to be lucky growing them, though. Last year I was given some, and I thought maybe I would be third time lucky trying to grow them. They did grow and flower, and I thought I had it cracked. However this year I got leaves only and not a single flower. Where did I go wrong?