A zoomed 5.0 for 12 hours is good. Be sure the cham can get under the light at a distance of 6" - 8" away. The intensity of these bulbs diminshes with distance. THey also diminish with time so be sure to replace the bulb every 6 to 9 months.
Also , consider placing the light at one end of the cage, so that the cham can "escape" the UVB when it prefers to avoid it. Chams will regulate their own exposure , as needed for D3 synthesis allowing calcium absorption, by seeking out or avoiding direct UVB exposure.
Also, be sure that the UVB source is not shining through any glass or plastic cage top or light fixture lens, as this will filter out the UVB.
And, be careful to NOT overdose your cham with supplements, especially D3.
Check other threads for recommended supplementation schedules. Personally, I dust with calcium/D3 twice a week. Calcium without D3 all other day. And I dust with Herptivite and MinerallO twice a month.