they can be pruned at any time. i prune mine whenever they need it. they can take heavy pruning. it makes them produce more fruit

most people prefer to prune after loosing the leaves, often in late winter or early spring just before it flowers

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Guavas can take heavy pruning, however, and can be used as informal hedges or screens. Since the fruit is borne on new growth, pruning in late winter or early spring does not interfere with the next year's crop. Prune in February or early March, opening the center of the tree, to increase fruiting.

http://garden.org/nga/searchqa/answer/23076/

You might want to wait until spring since yours is potted and brought indoors or sunroom? Like Larry says- they are very prunable. YOUTUBE has a few on how to prune outdoor Guavas to keep them from getting leggy or too tall.