Provided no frost is due they can be left out all the time.

I agree...also if its raining very heavily....they might get a bit swamped..I am still keeping mine under cover at night,but with the front open on the growhouses..

Scrumpy and Bloomer are right. You sound worried about occasionally leaving them under cover, and that's fine, so long as you bring them out most days.

Thank you for your replies. Not so much worried but I've put a lot of work into growing all my seeds and just wanted to make sure they weren't going to come to harm with this stupid weather. Are we ever going to get some warmer days :-( .

I strongly disagree with saying to leave them out all the time just because frost is no longer a threat,

The early morning mist and damp plus all this rain rain rain will not harden the young plants off it's drowning the roots, and washing any goodness out of the comost.

the idea of hardening off is a gradual thing to get the plants use to the cooler outside climate not to drown the roots and then cool them right down to the early morn climate.

You've spent both time & money buying & growing these seeds now dont waste it all,

put the seeds out all day "if the weather is not cold you dont just need frost to stop these young plants in there tracks,
continuing wet conditions will cause damage"

Wait until the weather has warmed up all day and the nights are not as cold as they are now,
if you do want to leave the plants out all night! then use a small tunnel to cover them.
Your seeds your money spent and your efforts gone into getting to the stage your at now "Dont spoil it".

In 30 years of growing plants I have not lost one when hardening off. PDB has already started the process and I would guess has advanced plants.
Rain damage/damping off will only occur on very young seeds. Established plants in pots will not suffer at all.
No matter how hard it rains, you'll still need to water plants in pots. My geraniums that in theory have had a good soaking from the latest monsoons were actually quite dry in the compost.