How long would you heat a shepherd's pie for?

[toastofthetown]

Made a large veggie shepherd's pie yesterday for today. Recipe says to oven cook for 25 minutes, but that's assuming the components are hot, so how long would you adjust time for?

I would microwave it until it was hot in the middle, then finish it off in the oven or under the grill to crisp up the top.

That or put it in the oven for 30 to 40 minutes until its hot in the centre.