It is crucial that you stick to the time limits. For most cases, applications must be made within three calendar months of the alleged breach of the law. For unfair dismissal cases, this is three months from the 'effective date of termination' (usually the day on which you finish work), but there are a few variations (for example, six months to claim redundancy payment).
The correct way to calculate the three month period is to take the day immediately before the dismissal date and to go forwards by three months. So for example, if someone is dismissed on 21 May, the three month deadline ends on 20 August, not 21 August.
Tribunals only rarely agree to extend time when time limits are missed.
The first step in a tribunal claim is now to submit an Acas Early Conciliation Notification Form. This step must be completed inside the three month window.
One benefit of an online claim is that it provides good evidence (an automated response) showing that the claim was submitted in time. In any event, it is very important not to leave the claim until the last minute. Tribunals never accept the last minute failure of electronic equipment such as your computer or internet connection as a good excuse to justify missing the deadline for an unfair dismissal claim.
If you make the claim by post, use registered post.