I think it depends on what state you are in TABSportsbet in NSW allows you to place multi bets up to 10 legs with odds of less than 5000/1. On the bet types they offer only. some of the other bookie sites allow multis of your or their choosing with multiple options and legs.

No 24 hour restrictions that I have come accross. They do have restrictions on some of the bets, for instance:

eg;

TABSportsbet NSW - You can't bet on Roosters to beat Penrith and take the Roosters 1-12 in the same multi.

or

Australia to beat NZ in 2nd test and Ponting to score most runs in the game.

I am unsure of the rules for most of the other bookie sites.

I hope this helps.

Here is the best one I have gotten home on in recent weeks:

Chelsea $1.85 Vs Barcelona
x
Lyon $1.92 Vs Weder Bremen
x
AC Milan $1.92 Vs Manchester United
x
Arsenal $2.10 Vs Bayern Munich
x
Juventus $2.10 Vs Real Madrid
x
Australia $1.63 Vs New Zealand (cricket, 1st test result)
x
Carlton $1.42 Vs West Coast Eagles (AFL Wizard Cup Grand Final)
x
Sydney Kings $1.85 Vs Wollongong (to win NBL Grand Final series).

Odds = $128.78
x
My Bet: $10.00

Return: $1,287.80