"tentatively by" is a correct and usable phrase in written English.
It is typically used when referring to a deadline for something. For example, "The project must be completed tentatively by next Friday."
They started tentatively by adapting a play, Falsch, in 1986.
So we'll postpone the moving problem tentatively by half a year.
Lower critical solution temperature behaviour of the melts could be determined tentatively by optical inspection.
The explanation, proffered tentatively by Bergner, is that female sexuality is as raw and bestial as male sexuality.
The cycle was sung here, sometimes tentatively, by three promising singers: Lei Xu, a soprano; Nathalie Mittelbach, a mezzo-soprano; and Spencer Lang, a tenor.
And earlier this month the Tory defence and foreign shadow secretaries, Liam Fox and William Hague, are reported to have lobbied successfully against the idea – floated very tentatively by David Cameron – that Britain's nuclear deterrent might be questioned.
The law would be similar to one passed last month by Pasadena and another tentatively approved by West Hollywood.
The diarist John Evelyn called him a Scotsman, an epithet repeated by Horace Walpole and tentatively accepted by his later biographer, Verne.
In 2009, a fairly generic set of competencies was tabled by the National Public Health Education and Research Program and tentatively accepted by participating public health institutions.
This V2' peak is tentatively explained by the formation of chains by beads bound in DNA coils.
This phenomenon was tentatively explained by the abundance of vapors generated by the action of the laser.
