I pretty much support this approach. I tell my students and post-docs that we have project deadlines that we need to meet and as long as we meet them I don't care what office hours they keep or if they take vacation etc., in fact I encourage them to take the time they need...but there will be problems if the contracted project deadline is missed because they failed to get their work done. Only real difference is that we are not talking about month to month quotas or deadlines, these are semi-annual or annual reporting requirements to the contract sponsor or multi-year project contracts, so taking an extra week in January to rest and relax, can easily be covered before the final report deadline in September. But it you take an unplanned 10 days off 2-weeks before a project end date that can require some paperwork.I tell my team to take as much time as they want, again knowing they are responsible for the quota. I also suggest they track the exact number of days so they can be sure to use at least 3 to 4 weeks a year. it's really easy to not use as much as you should when you don't have to put it in a tracking platform.