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A meditator has heard that deep peace can be reached only once and never again. Ajahn Dtun says he has never heard the Buddha or the arahant disciples teach such a thing, so why believe someone with wrong view? One meditates to make the mind peaceful, and when it becomes peaceful one should let it rest there for as long as it stays, without wondering what to do next. When the mind withdraws and starts thinking, that is the time to take up the body and contemplate its impermanence, like sleeping fully at night and working after waking, or letting a phone battery charge before using it.
He warns not to believe the defilements when they say the peace cannot return. Like a child learning to walk who falls and gets up again, one begins anew each day, returns to the breath or buddho, sets aside past and future and keeps practising with patience (khanti) and effort (viriya). Comparing with a peaceful sitting from the past only obstructs the mind, a kind of saṅkhāra-māra; accept whatever peace arises.
At the end of a sitting, whether it was peaceful or not, he advises reminding oneself that both peace and restlessness are impermanent and letting go of both. To keep samādhi throughout the day, sit and walk often, like recharging a battery, as the meditation monks do from morning to night. Lay people with work and families can start with ten minutes and gradually increase: a small investment brings a small return, a larger one a larger return.