For ayambil, boiled water is generally taken fresh after it has cooled. In many Jain traditions, it is used the same day and not kept for long; some follow a limit of up to about 24 hours, but this can vary by sampraday and local ayambil vidhi.

So the safest Jain practice is:

• Boil clean water
• Let it cool naturally
• Drink it fresh, preferably the same day
• Follow the specific rule of your temple, guru, or local tradition

If you want, I can also explain the usual Jain rules for ayambil food and water in simple points.