if you are going to spray on a flowering plant, might as well use something that is effective.
pyrethrines have a half-life of 2-3 days? If you have 15+ days left, vast majority would be gone. This would probably be dafe.
"In the presence of sunlight, pyrethrin 1, a component of pyrethrins, breaks down rapidly in water and on soil and plant surfaces. Half-lives are 11.8 hours in water and 12.9 hours on soil surfaces. On potato and tomato leaves, less than 3% remained after 5 days. Pyrethrins do not readily spread within plants."
- http://npic.orst.edu/factsheets/pyrethrins.html
So, 3% isn't enough, but shows how fast it breaks down. 2 weeks would probably be safe... safer than neem oil that is 2-4 day half life - http://npic.orst.edu/factsheets/neemgen.html
lets assume 2 days half life over 2 weeks, which simplified is
.5^7 = all but .78125% would be there... not saying this is safe. some things will be danagerous at very low levels, especially things that are typically effective at killing pests.
the pyrethrins would be.. lets go with 12 hours, so .5^28 over 2 weeks is .0000003725% remaining.