The DfES regulations state that these four terms are "not measured as an accumulation of days worked but in calendar months from the first day of the first casual supply post. After four terms, the NQT's next teaching post must be one where induction can be started" (DfES Guidance 5822001).
The time limit starts on the first day that you worked as a supply teacher and finishes four calendar terms later. The fact that you only did six days' work makes no difference to the fact that you are near the end of the time limit for supply.
Exactly when this time is up is a difficult point. I presume you did the six days in July 2001. Thus, one might argue that your supply teaching time limit runs out in December, or if someone was being awkward they could say that this coming term is the fifth one since starting supply, in which case your time is already up. I should assume the former.
Another point to consider is whether you had qualified teacher status when you did your supply work. Look at the date on your DfES certificate; if it is after you did supply, then you must have been working as an unqualified teacher, and thus have used none of the four-term time limit.
The five-year limit is pertinent to you. The regulations say: "The induction period is made up of three terms, but there can be gaps between these. Once started, the induction period should normally be completed within five years. If it lasts beyond this, the NQT may apply to the appropriate body for an extension not exceeding a full induction period" (DfES Guidance 5822001 paragraph 83).
You need to complete induction within five years, otherwise it may be extended further, but not necessarily. It would be up to you and the local education authority in its role as appropriate body to decide. In most cases, it would be advisable because it would be very hard to come back after such a long gap. You can, of course, take 10 or 20 years to complete induction. There is no time limit on it, contrary to popular opinion. It just means that after a gap of five years you can ask for an extension.
Are you a student or NQT? Email your questions to: email@example.com. Sara Bubb's A Newly Qualified Teacher's Manual:how to meet the induction standards is published by David Fulton, pound;5