you could keep this up for a while but after a couple months, you'll start feeling really shitty on the week off. Ideally, take them 1-2x per week and you'll be fine. The usual time for benzo physical addiction is 1 month, for a regular user, with no experience of benzodiazepines. For others, like me, it can take as little as a week of daily use to get you physically dependent.
^if you've never used benzos before then 1 month is the absolute max, if you've been doing this for a while, i wouldn't do more than 2-3 days at a time then a week break because valium stays on your receptors for a long time. A 2 week stint from a normal benzo naive user would probably not lead to any symptoms but if you've been an addict before you can expect a mild shitty withdrawal, no sleep, meat backs for back, anxiety, restlessness, delusions, shaking, stomach issues, no apetite and other fun stuff.
oh yes, for valium the withdrawal will kick in about 3 days after your last dose IME. depends on your metabolism and experience with valium though.