In the first part of the sentence--the part which you already understand--it mentions a "return." Return has several meanings, but in this sense, it means a sort of income or payment (not always financial.)
In the second part of the sentence, the author clarifies which types of returns he or she's talking about:
"be this in terms of pleasure, work value, or rest."
So, it's basically saying that "we begin to move restlessly about if we feel time is slipping away without a return related to pleasure, a return related to work value, or return related to rest."
"Be this in terms of" is a linguisticly-complicated way of saying "related to."
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