Yes, if is possible for your Fomantis to evolve at a later level. You should just need to level it up once during the daytime. All Pokemon can evolve by leveling up if they're above the level they start to evolve at. The only thing that would prevent a Pokemon from evolving by leveling up above the level they start to evolve at (Assuming that the Pokemon is not holding an Everstone and has all of the right conditions it needs to evolve, such as knowing a certain move, holding a specific item, or being leveled up at a certain time of day.) is if they are at level 100 and cannot level up anymore.