yahoo transaction rules:
The deadline to complete all transactions (trades, waiver claims, and free agent claims) for a given week is 11:59 pm PT every Sunday.
However, you will only be able to add players to your active roster for the current week if the transaction is completed no later than five minutes before the start of the player's game. In other words, none of the active players on your team (players in a starting roster spot) involved in a move can have played or be within five minutes of their game's start time, or the transaction will not be allowed. So, for example, transactions for all active players who play at 10:00 am PT must be completed by 9:55 am PT.
You will be allowed to make transactions involving your bench players at any time during a week – even if a player's game has begun. However, you will not be permitted to activate any player who is already within the five-minute limit. All such players will have to remain on your bench until the following week.
Additionally, all intra-roster moves (switching players between active and bench spots) can be made until five minutes before the start of each player's game.
Also, bear in mind that your league may include a trading deadline. Click on the League Settings link from your league home page to view the configuration of your league. Trade deadlines do not impact the ability to add players via waivers or free agency.
yahoo roster rules:
1. You do not have to start a player at every roster position, but fantasy points and statistics will only be accumulated by those players on your starting roster.
2. Players are only eligible to play at those position(s) designated by Yahoo! Sports.
3. If you pick up a player, but later realize you did not want him on your team, you may immediately waive him. However, you can only claim and waive the same player two times every 24 hours
4. All active players earn fantasy points for all of your league's categories (you do not receive points for players on your bench). Points coming from categories not normally associated with a player's position (e.g., a kicker who throws a touchdown pass) are called miscellaneous points and are indicated by an * to the right of a player's point total.
5. All managers can set rosters for weeks in the future by going to the proper day on their team page and making the needed changes. However, all future lineups will be lost if a current player is dropped or traded, or if a new player is added to the current roster. So, if during Week 2, you submitted a roster for Weeks 3 and 4, but then go and pick up a free agent for Week 1, your future lineup changes will all be lost even though they had been saved earlier.