I always monitor our outside temps Pia..so you should do the same, even if it is grown indoors. When I know it would be more of a cloudy day, I keep the curtains open..but typically our summers here are hardly like that..always sun, sun, sun..so shaded always in the afternoon. Only in Fall to Spring when temps cools down, then I can safely open the curtains. It helps to have an indoor/outdoor sensor, so you can more or less see if it is getting too hot indoors & outdoors. And run some fan there, it will appreciate good overall air circulation.
Your next consideration will be during late Fall to Winter. Later on, you might consider putting them a bit further away from the window, the glass is too cold, so sit them maybe on a table beside that ledge when the colder season comes.
