I have had that situation all Liam's life due to toddler activities, although Liam is a bit older. What I tend to do is bring the nap forward 15mins of so & have myself ready , so the last thing I do is get Liam out of his cot & we go, then the next nap is also slightly earlier to make up for the short first one & when he had a catnap, I let that one go longer & gave one in the early days when we dropped it &/or brought bedtime forward so his awake time in the evening wasn't too long.... I only came unstuck when we started having 2 days in a row where I had to do, it... so I changed the day of one activity & now we do it 2-3 times a week & it works fine, so if you have to do it once, I doubt it will mess to much.