Maximize Velocity — ruling 1

You must still follow any timing restrictions and permissions when casting a spell with jump-start, including those based on the card's type. For instance, you can cast a sorcery using jump-start only when you could normally cast a sorcery.

Maximize Velocity — ruling 2

A spell cast using jump-start will always be exiled afterward, whether it resolves, it's countered, or it leaves the stack in some other way.

Maximize Velocity — ruling 3

If an effect allows you to pay an alternative cost rather than a spell's mana cost, you may pay that alternative cost when you jump-start a spell. You'll still discard a card as an additional cost to cast it.

Maximize Velocity — ruling 4

If a card with jump-start is put into your graveyard during your turn, you'll be able to cast it right away if it's legal to do so, before an opponent can take any actions.

Maximize Velocity : règles, fonctionnement et interactions (MTG)

Maximize Velocity is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Target creature gets +1/+1 and gains haste until end of turn. Jump-start (You may cast this card from your graveyard by discarding a card in addition to paying its other costs. Then exile this card.)

How it works : Maximize Velocity

Original English text — Wizards of the Coast / Scryfall

#1October 5, 2018· Wizards of the Coast
You must still follow any timing restrictions and permissions when casting a spell with jump-start, including those based on the card's type. For instance, you can cast a sorcery using jump-start only when you could normally cast a sorcery.
No other card is named in this ruling.
#2October 5, 2018· Wizards of the Coast
A spell cast using jump-start will always be exiled afterward, whether it resolves, it's countered, or it leaves the stack in some other way.
No other card is named in this ruling.
#3October 5, 2018· Wizards of the Coast
If an effect allows you to pay an alternative cost rather than a spell's mana cost, you may pay that alternative cost when you jump-start a spell. You'll still discard a card as an additional cost to cast it.
No other card is named in this ruling.
#4October 5, 2018· Wizards of the Coast
If a card with jump-start is put into your graveyard during your turn, you'll be able to cast it right away if it's legal to do so, before an opponent can take any actions.
No other card is named in this ruling.