The phrase 'allot something to' is followed by a gerund ( V ing). In this sentence , the preposition 'to' is part of the verb phrase which precedes it (allot most of my time to..) , so the next word should be 'teaching'. That said, it's actually rather an awkward wording. 'Allot' is not a word we use much in this kind of context. We'd be more likely to say, "I devote most of my time to teaching". Note that it's the same construction: devote x to y (Ving).