You're confusing the 90 day validity period for the visa with how long a stay it grants. Single entry tourist visas are valid for use to enter Thailand once within 90 days from the day it is granted, but only give a 60 day stay once used to enter the country. You can extend it one time for 30 more days at immigration offices within Thailand for 1900 THB.
you clearly don't know what Thailand calls its various entry schemes. Visa on arrival and visa exempt entry are entirely different things. Visa on arrival is required for less than 20 nationalities, where they must PAY for a visa on arrival into Thailand, which grants only 15 days stay and is not extendable. Visa exempt entry is a free entry available to about 60 nationalities, granting a 30 day stay, which is extendable for 30 more days.
You are confused about Thailand's different entry schemes. USA passport holders qualify to enter via either a 30 day visa exempt entry (no need for a visa) by just showing up, or with a 60 day tourist visa granted in advance from a Thai consulate outside Thailand. If residing within the USA, the tourist visa can be applied for online via Thailand's e-visa website. Either the 30 day visa exempt entry or the 60 day tourist visa can be extended one time at immigration offices within Thailand for 30 additional days. Americans don't qualify for a separate entry scheme called visa on arrival, which some nationalities must use, where they pay for a visa when they get to Thailand, which grants only a 15 day stay.
Lazada has official brand shops for most retail brands. If you are worried about counterfeit SD cards, buy them from Sandisk Official, Kingston Official, or from the major electronics chains' official stores on Lazada, such as Powerbuy or Banana IT. Considering the frequent coupons and sales, it makes no sense to have such items sent from overseas when the actual manufacturer has direct shops on Lazada. Same applies to many other consumer goods brands. Just type a term like Sandisk Official, or Colgate Official, or other such term, and Lazada shows you the official store in their results.
no official time. But every entry is at the discretion of the immigration officer, and you can't expect to keep using visa exempt entries or tourist visas as a way to live in Thailand long term. Even spending several months away isn't enough to ensure entry, as your previous stay and entry history will all be considered.