Crypt. x Willissii is not as fast growing as the Crypt. Wendtii-types......and often a slow starter, needing to grow a strong root-system, before really getting into growth. Supposing you have a rich substrate, you should see begiining growth after 3 months, though.
Some root-fertiliser-capsules could help (and won't hurt, for sure) to "get things going". If plants look healthy, patience is the best medicine
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Andy; your plants are not Crypt. x Willissii !!!
Most likely Crypt. Wendtii 'green', which comes in several different types, with quite different hights. Personally, I actually prefere the lower growing ones, since there are so many higher growing Crypts. to choose from.