The II Future is used instead of the I Future in denoting Future time not belonging to the current day when the word avara is used together with a word expressing division of time, but not when it is a word giving the sense of 'day' or 'night'.,
The whole of the last sutra should be read into this. The difference between this and the last sutra is, that sutra 3.3.136 referred both to the limit of space and time, while sutra 3.3.137 refers to the limit of time only; moreover with regard to time, there is exception with regard to the portions of day and night. The yoga-vibhaga, the separation of this sutra from the last, is for the sake of subsequent aphorisms. Thus योऽयं संवत्सर आगामी तत्र यदवरमाग्रहायण्यास्तत्र अध्येष्यामहे 'in the month of Chaitra, the year after next, we shall read together'; तत्रोदनं भोक्ष्यामहे 'we shall eat rice then &c'.
This construction is, of course, only valid in denoting future time, otherwise not. Therefore not here: योऽयं वत्सरोऽतीतस्तस्य यदवरमाग्रहायण्यास्तत्र युक्ता अध्यैमहि 'in the month of Chaitra, the year before last, we read together'; तत्रौदनमभुञ्जमहि 'we ate together &c'.
Why do we say 'limit'? Observe योऽयं निरवधिकः काल आगामी तस्य यदवरमाग्रहायण्यास्तत्र युक्ता अध्येतास्महे--तत्रोदनं भोक्तास्महे ।
The limit must be 'on this side i. e. अवर side'. With the वर side limit, this rule will not apply. With the word पर, this construction is optional. See the next sutra.
Why do we say 'when not divisions of day and night'? There are three sorts of counter-examples in this case; as, योऽयं मास आगामी तस्य योऽवरः पञ्चदशरात्रः or योऽयं त्रिंशद्रात्र आगामी तस्य योऽवरोर्द्धमासः or योऽयं त्रिंशदहोरात्र आगामी तस्य योऽवरः पञ्चदशरात्रस्तत्र युक्ता अध्येतास्महे तत्र सक्तून् पातास्मः । Here Lut; or First Future has been employed and not the Second Future.,