SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51de59002f67fe2e938de31187d4a840a2650ec21ca66102cb00133cd3182dd4' 
  AND token = '1i5sOmbEGlYgaxry/JUQ6GlnIlDWX8uLr+vvmdmY3+Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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