context: The two groups had different strategies. IMARO as originally conceived sought to prepare a carefully planned uprising in the future, but the Supremacists preferred immediate raids and guerilla operations to foster disorder and a precipitate interventions. On the other hand, a smaller group of conservatives in Salonica organized a Bulgarian Secret Revolutionary Brotherhood . The latter was incorporated in IMARO by 1902 but its members as Ivan Garvanov, were to exert a significant influence on the organization. They were to push for the Ilinden-Preobrazhenie Uprising and later became the core of IMRO right-wing faction. One of the founding leaders of IMARO, Gotse Delchev, was a strong advocate for proceeding slowly, but the Supremacists pressed for a major uprising to take place in the summer of 1903. Delchev himself was killed by the Turks in May 1903. Meanwhile, in late April 1903, a group of young anarchists from  the Gemidzhii Circle - graduates from the Bulgarian Men's High School of Thessaloniki launched a campaign of terror bombing, the so-called Thessaloniki bombings of 1903. Their aim was to attract the attention of the Great Powers to Ottoman oppression in Macedonia and Eastern Thrace. As a response to the attacks, the Turkish Army and bashibozouks  massacred many innocent Bulgarians in Thessaloniki, and later in Bitola.
question: What time of year did the Thessaloniki bombings take place?
answer: April 1903