Guinea pigs outside?

belisha-beacon

Slightly off-topic because I know the main issue is whether they could go outside at this time of year (I personally wouldn't put them out), but my comment is more about the rest of the year.

I don't know your conservatory so it might be a different design to normal, but I'd absolutely recommend against putting any guinea-pig in a standard conservatory. In summer they can get unbearably hot and cause all sorts of health problems including stress and heart attacks. (It's like dogs in hot cars) If the conservatory is the only place they can suitably go in your house, it might be worth thinking about not getting any at all - sorry to say it.