Suspect that would not take very long since each project has N slots with work in the distribution system. If there momentarily is no work for eg opn1, it would default to your second choice and so on. Not sure if that's your expectation.

On Feb 9, 2020 I requested on github that BOINC add commands. Doubt it will ever happen.
BOINC grids such as WCG & LHC are mixing very different kinds of projects under the same Prefs. E.g., WCG now has two projects that require a fast turn around; the serial FAH2 and long ARF with sparse checkpoints. Clients need more effective ways to control their work.
Please add BOINC commands <maintain> & <priority> that tell the server what to do.
```
<app_config>
<app>
<name>ATLAS</name>
<!-- Xeon E5-2699 v4 22c44t 32 GB RAM L3 Cache = 55 MB -->
<maintain>18</maintain>
<max_concurrent>16</max_concurrent>
</app>
<app_version>
<app_name>ATLAS</app_name>
<plan_class>native_mt</plan_class>
<avg_ncpus>1</avg_ncpus>
<cmdline>--nthreads 1</cmdline>
</app_version>
<app>
<name>sixtrack</name>
<maintain>9</maintain>
<max_concurrent>6</max_concurrent>
</app>
<app>
<name>Theory</name>
<maintain>44</maintain>
</app>
<app>
<name>CMS</name>
<maintain>0</maintain>
</app>
</app_config>
```

And even better would be:
```
<app_config>
<app>
<name>ATLAS</name>
<!-- Xeon E5-2699 v4 22c44t 32 GB RAM L3 Cache = 55 MB -->
<priority>1</priority>
<max_concurrent>16</max_concurrent>
</app>
<app_version>
<app_name>ATLAS</app_name>
<plan_class>native_mt</plan_class>
<avg_ncpus>1</avg_ncpus>
<cmdline>--nthreads 1</cmdline>
</app_version>
<app>
<name>sixtrack</name>
<priority>3</priority>
</app>
<app>
<name>Theory</name>
<priority>2</priority>
</app>
<app>
<name>CMS</name>
<priority>0</priority>
</app>
</app_config>
```

I've just checked my task queue to find it is rammed with the Microbiome project, and the Covid19 tasks are having to wait and possibly expire. I've now had to come into my settings and untick get work for other projects and only tick covid19.

I just went to "My Contribution" page and under "My Projects" unchecked everything except Covid19. When the Covid19 is done i'll just go back and check the projects I was previously running.

Prioritising one project is simple with device profiles. You just uncheck all other projects but leave the option to get other work when your preferred project has run out. Setting a 2nd priority would be a problem. If you set a high cache for your preferred project would enable you to continue that project after it has run out.

Mike