SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '794383c75a9376e29f53744501c018a8051554804a353d247f0d71e66037b281' 
  AND token = '0douRhsvpDapBCQXKdvo7qLUUbjq2igHF3G8zliUyAs=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00032

JSON explain

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