I have come across the term 'Samayachara' but not sure what is it. (Read it in relation to 'Shri Vidya').
The word Samaya comes from 'sAmyam yAti' meaning that the equality of Shiva and Shakti is the essence of the Samayachara. There are five types of equality according to Lakshmidhara: Adhisthana-samya,avasthana-samya, anusthana-samya, rupa-samya and nama-samya.
In the worship of Sri-Vidya, there are three ways(Matas)-- Samaya-chara, Kaula-achara and Mishra-achara.
In the commentary of the Saundaryalahari (sloka 31), Lakshmidhara writes
The graceful God Pasupati has recommended different Tantras for the four main and mixed varnas. These Tantras are NOT for the brahmins following the Vedas.For the followers of the Vedas,Lord Pasupati has composed 'Suva-Aagama-Tantra-panchaka'. Vasishtha,Sanaka,Suka, Sananda and Sanatkumar--these five munis have followed this path known as the 'Samaya-aachaara'.
The basic texts of the Samayachara are Vashishta-samhita, Sanaka-samhita, Suka-samhita, Sanandana-samhita and Sanatkumara-samhita, also known as the shubha-Agama-Panchaka.
Sri Panchanana Tarkaratna writes in this regard
Samayachara involves only Manasa-upaasana or Internal Worship.There is no provision for external worship. They treat the the body of the aspirant with shat-ckras as the real Sri-Yantra.
So the Samayacharis do not have any purascharana, japa, homa or external pujavidhi.
There is no restriction on the Kaulaachari-s also.Lakshmidhara opines that yogis who concentrate on the sushumna are the real kaulas. However, some samayaacharies do not accept the Kaulaachaara as a path to be followed by the Vedic brahmins.
Different stages of Samayacahara according to the Parasurama-kalpasutra are :arambha,taruna,yauvana and prauda. Then starts 'Svairachara' where the sadhaka goes beyond any scriptural restrictions.
As the Parasurama-kalpasutra mentions:
samayo guptah sanketah sAdhanapaddhatih..samayo rahasi proktah kAle karmakshame api cha (vritti of 7.1) meaning that samayachara is a hidden form of spiritual practice which is revealed on due time to the deserving aspirants.
So much information beyond the above is neither available or be expected to be availabe publicly as per the scripture.
According to some views, Sri Adi Shankaracharya Himself did practise Sri Vidya Upasana following the Samayachara.
Reference: Sastramulak Bharatiya Shaktisadhana, Upendrakumar Das,RMIC, Vol.1, chapter 12.