Which Shastras say that we should not eat after Sunset?

Question

In one of the discourse or dialogue, Jagadguru Shri Chandrasekharendra Saraswati Mahaswamigal, while describing the good qualities of crow, said

It wakes up at Bramhamuhurtam……it caws and wakes you up…..even cocks may not wake up on time many a days- they are moody…but a crow is on time…it says “kaka” and wakes you up at Bramhamuhurtam, an apt time to perform japam. It is such an amazing guide for pooja, is it not?
Further, it calls other crows when it gets food…..a quality not seen in other creatures, teaching humans to share their food. Then in the evening before it sleeps, it again says “kaka” to thank god for all that happened that day! Also crows don’t eat after Sunset, a practice reiterated in Shastras…….. How many people follow this?

Source

Which Shastras say that we should not eat after Sunset?
Why, we Vedic Hindus are not following this then?

Also, if some one is doing Sayam Sandhya Vandana, should he eat before doing it as it is done at sunset? But while doing it, shouldn't the stomach be preferably empty, which takes around 4 hours, so if the sunset is at 6pm, so one should not eat anything after 2pm? Is there any recommendation in scripture as to how many hour gap should be there between meal and Sayam Sandhya Vandana?

Answer 1

Meal timing slots between sunrise-sunset given in vedas and mahAbhArata:

shatapatha brahmana 2:4:2 :

2:4:2:3 athainam manuṣyāḥ | prāvṛtā upasthaṃ kṛtvopāsīdaṃstānabravītsāyam prātarvo 'śanam prajā vo mṛtyurvo'gnirvo jyotiriti

2:4:2:3 Then the men approached him, clothed and bending their bodies. To them he said, 'Your eating (shall be) in the evening and in the morning; your offspring your death; and the fire (Agni) your light!'

2:4:2:6 naiva devā atikrāmanti | na pitaro na paśavo manuṣyā evaike'tikrāmanti tasmādyo manuṣyāṇām medyatyaśubhe medyati vihūrcati hi na hyayanāya cana bhavatyanṛtaṃ hi kṛtvā medyati tasmādu sāyamprātarāśyeva syātsa yo haivaṃ vidvāntsāyamprātarāśī bhavati sarvaṃ haivāyureti yadu ha kiṃ ca vācā vyāharati tadu haiva bhavatyetaddhi devasatyaṃ gopāyati taddhaitattejo nāma brāhmaṇaṃ ya etasya vrataṃ śaknoti caritum

2:4:2:6 Neither the gods, nor the fathers, nor beasts transgress (this ordinance); some of the men alone transgress it. Hence whatever man grows fat; he grows fat in unrighteousness, since he totters and is unable to walk because of his having grown fat by doing wrong. One should therefore eat only in the evening and morning; and whosoever, knowing this, eats only in the evening and morning, reaches the full measure of life; and whatever he speaks, that is (true); because he observes that divine truth. For, verily, that is Brâhmanic lustre (tegas), when one knows to keep His (Pragâpati's) law.

taittiriya sanhita vi. 2. 5 :

Milk (is the drink) of the Brahman, the Brahman is brilliance, milk is brilliance; verily by brilliance he endows himself with brilliance and milk. Again by milk foetuses grow; the man who is consecrated is as it were a foetus; in that milk is his drink, verily thus he causes himself to grow. Manu was wont thrice to take drink, the Asuras twice, the gods once . Morning, midday, evening, were the times of Manu's drinking, the symbol of the sacrifice of cooked food, (serving) for prosperity.

mahAbhArata anusasana Parva CLXII :

Two times have been appointed by the deities for human beings to take their food, viz., morning and evening. During the interval one should not eat anything. By following this rule about eating, one is said to observe a fast.