When time is of the essence, you need to act quickly. However, there are many other ways to express this sense of urgency in writing or conversation. You might say that something is critical, imperative, or crucial. If you need to act swiftly, you could use words like urgent, pressing, or time-sensitive. Another alternative might be to say that something is vital, indispensable, or important. Essentially, all of these phrases convey the same idea - that time is running out and action is essential. So whether you're trying to meet a deadline, catch a flight, or respond to an emergency, these synonyms can help you to convey the urgency of the situation.