welcome! the best fertilizer to use is regular old department store Miracle gro or the equivalent. Anything marked "bonsai fertilizer" is overpriced and not really any more effective than regular commercial fertilizers. Such pelletized ferts are low dose and take time to break down enough for the tree to use. Such ferts are typically used on older more developed trees to prevent wild growth.
All this said, since you've repotted, fertilizers shouldn't be applied for a month or so, since the roots have been disturbed and can't really use it. Also, ditch the tray underneath the pot. It can cause trouble with drainage. Tree should also be outside. Can't tell if that's the case here.
Although Miracle Gro is cheaper and probably more effective the packet you have is still OK to use. Junipers can't read and don't really care where their nutrients come from.
The pellet ferts take a while to break down and release nutrients so I'd be quite comfortable with adding some within a week of repotting. The fact you are asking almost certainly means you are new to bonsai and therefore unlikely to have reduced roots very much so when and how much are less of an issue than with a tree that has had roots reduced severely.
The organic pellets also tend to disintegrate on the surface and look unsightly. Hard to remove after. Many growers fill tea bags or similar with the pellets and place that on the soils surface. Still allows the fert to release nutrient when watered but much easier to remove after a month or 2.
Not clear how large the tree and pot are as there's not much for scale in the photos but I'd guess about 1 tsp added every 4-6 weeks through the growing season should be OK but double that would not hurt as the organics are not so strong.
In some areas organics attract dogs, squirrels, etc. You may have to pin the fertiliser bags into the soil if they begin to disappear.
Consider supplementing the pellets with a liquid fert every 3-4 weeks as well. Liquid is immediately available and should give a welcome boost to the plants.
thank you both so much! Yes definitely outside, and the pot is approx 8x6 inches and 4 inches deep. I was just about to ask about the additional fertilizer! 6 months to me seems fairly iffy as far as lasting, I somewhat didn’t want to use the time release pellets for that reason. Would you go with a liquid additional monthly fertilizer thats low like a 333? Thank you again!