In one continuous period, but only with difficulty (10)

'only with difficulty' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'in one continuous period' is the wordplay.
I cannot quite see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is present in the answer.
'period' could be 'stretch' (stretch of time) and 'stretch' is found within the answer.
The remaining letters 'ta' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'but' is the link.

Can you help me to learn more?