Slots

Cardano measures time in slots. Each slot has a fixed duration determined by the network's configuration. The transaction builder converts between Unix timestamps and slots using the slot config.

Slot Configuration

Network	Slot Length	Start Time
Mainnet	1000ms (1 second)	Shelley era start
Preprod	1000ms (1 second)	Network genesis
Preview	1000ms (1 second)	Network genesis
Devnet	Configurable (20-100ms typical)	Cluster creation

How Conversion Works

The slot config defines three values:

• zeroTime — Unix timestamp of the network's start
• zeroSlot — First slot number (Shelley era)
• slotLength — Milliseconds per slot

The builder uses these to convert: slot = zeroSlot + (unixTime - zeroTime) / slotLength

Custom Slot Config

For devnet or custom networks, you can override the slot config in build options:

import { Address, Assets, preprod, Client } from "@evolution-sdk/evolution"

const client = Client.make(preprod)
  .withBlockfrost({
    baseUrl: "https://cardano-preprod.blockfrost.io/api/v0",
    projectId: process.env.BLOCKFROST_API_KEY!
  })
  .withSeed({ mnemonic: process.env.WALLET_MNEMONIC!, accountIndex: 0 })

const tx = await client
  .newTx()
  .payToAddress({
    address: Address.fromBech32("addr_test1vrm9x2dgvdau8vckj4duc89m638t8djmluqw5pdrFollw8qd9k63"),
    assets: Assets.fromLovelace(2_000_000n)
  })
  .build({
    slotConfig: {
      zeroTime: 1666656000000n,
      zeroSlot: 0n,
      slotLength: 1000
    }
  })

Manual Slot Conversion

import { Time, SlotConfig } from "@evolution-sdk/evolution"

const preprodConfig = SlotConfig.SLOT_CONFIG_NETWORK.Preprod
const mainnetConfig = SlotConfig.SLOT_CONFIG_NETWORK.Mainnet

// Unix time → slot
const now = BigInt(Date.now())
const currentSlot = Time.unixTimeToSlot(now, preprodConfig)
console.log("Current slot:", currentSlot)

// Slot → Unix time
const targetSlot = 50000000n
const targetTime = Time.slotToUnixTime(targetSlot, preprodConfig)
console.log("Slot 50M is at:", new Date(Number(targetTime)))

Available Network Configs

Network	SlotConfig.SLOT_CONFIG_NETWORK.X	Zero Time	Zero Slot	Slot Length
Mainnet	.Mainnet	1596059091000 (Shelley start)	4492800	1000ms
Preprod	.Preprod	1655769600000	0	1000ms
Preview	.Preview	1666656000000	0	1000ms

Next Steps

• POSIX Time — Unix timestamp utilities
• Validity Ranges — Setting time constraints