Samādhi is the mark of accomplishment in Dharma practice.

Question: When practicing the contemplation of the sun, must one practice until the image does not disappear for all 24 hours of the day before proceeding step by step to the next contemplation?

Answer: For each of the sixteen contemplations in the Contemplation Sutra (Amitāyurdhyāna Sūtra), the contemplative practice (vipaśyanā-caryā) is only considered complete after meditative absorption (samādhi) has manifested; after that, one can proceed to the next contemplation. The first contemplation, the sun contemplation, requires the attainment of samādhi — the setting-sun samādhi — in which the image of the setting sun in the mind can continuously appear without ceasing, and both body and mind are in a state of meditative concentration, free from afflictions and scattered thoughts. Apart from sleeping, one remains in samādhi at all times. Only then is the sun-contemplation samādhi complete, and one can move on to the second contemplation. In cultivating any dharma and realizing any path, including meditative concentration and wisdom, if samādhi does not manifest, it does not count as successful cultivation, nor as realizing the dharma or the path. In the period before and after samādhi manifests, sleep is no longer heavy; there are no scattered or chaotic dreams, and the mind has a certain degree of clarity. Sleep is brief and light, without dullness. In light sleep there should still be images; in deep sleep there are none.

We have been practicing the sun contemplation in our group for about three years now, haven't we? Not a single person has succeeded in it — and this is the simplest and easiest of the contemplative practices. This shows that cultivation is not such a simple matter, especially the attainment of great wisdom such as the eradication of the view of self (satkāya-dṛṣṭi-prahāṇa) and seeing the mind and realizing one's nature — these are even less easily accomplished. Of the sixteen contemplations in the Contemplation Sutra, only by accomplishing the third contemplation can one be assured of rebirth in the land of bliss (sukhāvatī) at the end of life, and only by reaching the seventh contemplation can one see the mind and attain enlightenment. In three years, no one has accomplished even the first contemplation — in what year or month will the third and seventh contemplations be accomplished? Cultivation is not such an easy matter, unless one has already practiced it in past lives and was an achiever; only then is it slightly easier in this life.