If the weather continues to be rather cool, you still can carry out most of the leftover tasks from March. However, I would say it is probably safer to stop repotting the deciduous trees from the middle and for evergreen trees from the end of April.
This is the best time to start air-layering evergreens such as junipers, Japanese black or white pines etc.
It is time to start your fortnightly fertilizing routine on your deciduous trees that have NOT been repotted. First with weaker Bonsai food then with a normal one until the end of summer to maintain a health and vigor of your trees.
DO NOT FEED NEWLY REPOTTED TREES UNTIL THEY ARE WELL ESTABLISHED AND GROWING.
If fertilizer is applied to a freshly repotted tree, the roots can rot.
During spring it is highly recommended to use a high-nitrogen fertilizer to promote leaf growth. Please remember, do not fertilize blooming bonsai until the flower has fallen.
April is the best time for taking an evergreen cutting, keep in mind when you trim your evergreen bonsai trees such as junipers Hinoki cypress etc. Use the thinning which have a hard-wood heel for making cuttings.
By the end of April all trees should be putting out new leaves and spring flowering trees should start to bloom.