SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a51d27d322201606df2663d25e363167eaf41a391dac2a7a25b7bc1ed6624b0c' 
  AND token = 'erSDoyBwXTk9LTyLkIQld2vkeoiW7SXKpmDPSUkmHhE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00038

JSON explain

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