SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a82314f78beaac263431e3280ef9d1256d685de54388db01d42b357a401344b8' 
  AND token = 'utmtTRznkmTWLghYHlgwKGgL2HiPzu1oeLzv+aSZTj8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}