The repair-time guarantee (GTR in France, tied to MTTR) is the contractual commitment to fix a failed link within a maximum delay: 4 business hours (the business standard), 4h 24/7, or even 2h on critical access. If exceeded, penalties apply — capped, so read them.
It is THE difference between dedicated business fiber (FTTO/FTTE) and shared consumer fiber (FTTH): FTTH costs 5 to 10 times less, but without a repair guarantee an outage can last days. Best practice is not necessarily paying for guarantees everywhere: on a secondary site, FTTH doubled with 4G/5G backup often delivers better real availability than a single guaranteed link — for less money. Reserve short repair guarantees for sites where every hour of downtime costs.