SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b2d6983b0dca1d8151064a6a3a7123bfe596abd4dd39e23989090857aac0cd52' 
  AND token = 'smlN4/W6xJ1EvgypPfOjgBkbLy+rF7KeVJJ3Qs6+KBg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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