Yes.
If you have not done so, you should more or less have settled on the type of bonsai media you want to use for deciduous trees, and broadleaf evergreen trees. The same mix you use for elms, maples, and ficus, will work for serissa. Key is moisture retention, and sifted for particle size, eliminating fines, which will give good air circulation to the roots.
Don't use an all inert mix like what is often used for pines. So just pumice, or a pumice & lava blend is better for pines, not the best for Serissa.
As soon as you have time, I would transplant your Serissa into the same deciduous mix you use for your other trees. That way you will be familiar with how long it takes to go from wet to dry. Makes proper watering easier to have only one or two different mixes for your whole collection.
Serissa, more so than most species can be repotted anytime from spring thru autumn without serious problems. Best repotting is done after summer solstice thru to autumn equinox. Also end of winter, just before spring flush of growth. They are pretty forgiving.
