不足 and 余裕: a shortfall and room to spare
Track staff shortages and spare time separately, using the required amount rather than a number alone to judge sufficiency.
Less than the amount needed
不足, read ふそく, means a shortfall relative to what is needed. 人手が不足しています。 says that there are too few people to do the work.
準備に必要な時間が不足しています。 says that there is not enough time for preparation. Read 時間 as the resource and 必要な as the requirement.
Room to spare in time or resources
余裕, read よゆう, means room to spare or a situation without immediate pressure. 出発まで時間に余裕があります。 says that there is time to spare before departure.
余裕を持って家を出てください。 asks someone to leave home with time to spare. The expression alone does not specify exactly how many minutes early to leave.
Different resources can have different states
人数は不足していますが、時間には余裕があります。 says that there are too few people, but time is ample. It is not a contradiction because it concerns different resources.
Having some stock does not always mean having enough. 用紙は十枚ありますが、必要な二十枚には不足しています。 says that ten sheets are available but fall short of the required twenty.
Is 人数は不足していますが、時間には余裕があります。 contradictory?
Show the answer and why
No. People are insufficient while time is ample, so both states can hold together.